Split lambda fueling operation systems and methods

ABSTRACT

Methods and systems for operating an engine with split lambda modes are provided. At least one example method comprises, while operating an engine in a condition that is within a resonant frequency region for a default split lambda mode, carrying out a rolling split lambda mode. The engine may be operated with only stoichiometric engine cycles in the default split lambda mode, the stoichiometric engine cycles including enleaned and enriched cylinders. Further, the engine may be operated with a plurality of non-stoichiometric engine cycles when carrying out the rolling split lambda mode, the plurality of non-stoichiometric engine cycles including at least one rich engine cycle and at least one lean engine cycle.

FIELD

The present description relates generally to methods and systems forcontrolling a vehicle engine with split lambda fueling operations.

BACKGROUND/SUMMARY

Modern engines are operated with a substantially stoichiometric air fuelratio over a large portion of an engine speed-load map to maintainemission control device efficiency and meet emissions requirements.However at higher engine speeds and loads, typically the fuel will bescheduled rich of stoichiometry to cool a catalyst of the emissioncontrol device, as excess unburned fuel may help to cool the engine andexhaust components. For example, in gasoline turbocharged directinjection (GTDI) engines, the turbo inlet temperature is typically thehottest component and must be controlled to stay below a maximumallowable temperature to prevent operation problems. However, when theengine is operated rich to enable such cooling, hydrocarbon (HC) andcarbon monoxide (CO) emissions may increase, and there is an associatedincrease in fuel consumption. Other attempts to address such emissionsand fuel consumption issues have included operating the engines atstoichiometry over all conditions to avoid the HC and CO emissionincrease associated with enrichment operation. Additionally oralternatively, load limit operations may be carried out, such aslimiting an engine speed, airflow, and torque output so that thesecooling operations are not necessary. Another proposed solution has beento carry out a split lambda fuel control scheme. In a split lambda fuelcontrol scheme, fuel delivery to the cylinders is enrichened or enleanedfrom stoichiometry while maintaining substantially stoichiometricconditions at the emission control device, so that emissions are avoidedand exhaust temperatures are reduced without sacrificing engineperformance. In some of these proposed split lambda fuel controlschemes, strategies such as providing exhaust gas recirculation (EGR) toan intake passage of the engine from a subset of the cylinders has beenproposed. In this way, engine power output may be increased by partiallyenriching the engine without increasing vehicle emissions.

However, the inventors have recognized that the above strategies haveseveral shortcomings, especially concerning maintaining engineperformance while avoiding noise, vibration, and harshness (NVH).

For example, previous approaches of operating the engine atstoichiometry over all conditions and load limiting strategies severelyreduce engine performance. Further, previous default split lambdaapproaches may result in pronounced NVH issues if the engine is operatedat a speed and load where the default split lambda pattern excites theresonance frequency and causes amplification of frequencies excited bythe split lambda fueling pattern due to resonance. As to previous splitlambda control schemes, the complex fueling strategy may create issuesconcerning accurately calculating a torque output. If the torque outputis not being accurately determined, engine performance may be reducedand NVH may occur. Moreover, these previous split lambda schemes alsofail to address issues of reducing NVH due to resonance amplification,and the above-discussed EGR strategy has little impact on increasingengine power.

In one example, the issues described above may be addressed by methodsthat may include carrying out a plurality of non-stoichiometric enginecycles while maintaining substantially stoichiometric conditions at anemission control device. By allowing non-stoichiometric engine cycles,additional fueling schedules with different frequencies (of repeatingpatterns of rich and lean cylinders) compared to those of stoichiometricengine cycles (with at least one rich or lean cylinders) are possible.In this way, NVH issues may be mitigated by choosing a fueling schedulethat avoids exciting the engine or powertrain resonant frequencies whilemaintaining engine performance and reducing emissions. The optimalfueling schedule may vary based on engine speed and load conditions.Furthermore, the rolling split lambda may be used instead of defaultsplit lambda whenever split lambda operation is required to enablehigher torques, and the rolling split lambda improves NVH compared todefault split lambda, and/or the rolling split lambda enables higherengine torques.

Such an approach as developed by the inventors may be advantageous forseveral reasons. For example, consider a 6 cylinder engine. Alternatingcylinders rich (R) and lean (L), each with equal rich and lean biasessuch as 20% each, results in a default split lambda as the cycle RLRLRLor LRLRLR is stoichiometric. The shortest repeating pattern (RL or LR)thus has a frequency three times the cycle frequency. Therefore, if, forexample, a resonant frequency at 3000 RPM is close to three times thecycle frequency, the default split lambda may cause undesirable NVH. Arolling split lambda where cylinder duplets alternate rich and leanRRLLRR-LLRRLL has a shortest pattern of RRLL or RLLR or LLRR or LRRL,repeating at 1.5 times the cycle frequency which avoids the resonantfrequency. However, if the engine speed changes to 6000 RPM, theresonant frequency now is at 1.5 times the cycle frequency. Therefore, adefault split lambda may be better for NVH at this condition.

Having a rolling split lambda option may allow split lambda operation inregions where it was not possible with default split lambda (as the onlysplit lambda mode) due to NVH. But this doesn't necessarily mean thatrolling split lambda is better for NVH and avoiding amplification due toresonance everywhere. Further, having the rolling split lambda optionmay thus allow split lambda operation in speed-load regions where it wasnot possible with default split lambda as the only split lambda mode dueto NVH. Thus, improvements over previous split lambda approaches may beachieved.

Further, as another example, consider a 3 cylinder engine. Due to theodd number of cylinders, a default split lambda mode is only possiblewith unequal rich and lean biases (for example, a 20% rich firstcylinder, a 10% lean second cylinder, and a 10% lean third cylinder), orwith running one cylinder stoichiometric (for example a 20% rich firstcylinder, a stoichiometric second cylinder, a 20% lean third cylinder).A 10% bias or 0% bias from stoichiometric as in the default split lambdamode results in higher exhaust temperatures than a 20% bias fromstoichiometric in the rolling split lambda mode. Thus, the rolling splitlambda mode described herein with alternating 20% rich and 20% leanbiases can further advantageously reduce exhaust temperatures and allowhigher torques.

Further, the issues described above may additionally or alternatively beaddressed by methods for calculating a torque output based on one ormore torque modifiers, the one or more torque modifiers including an airfuel ratio and spark timing. In particular, during a split lambdafueling mode, the torque output calculations may include calculating thetorque output for each cylinder separately and then summing the torqueoutputs. As another example, during a split lambda fueling mode, thetorque output of all lean cylinders may be calculated as a first group,the torque output of all rich cylinders may be separately calculated asa second group, and then the torque output of the first group and thesecond group may be summed. Such an approach to calculating the torqueoutput may help to ensure accuracy during split lambda fueling modes,such as the default split lambda mode and the rolling split lambda modediscussed below.

Further, in addition to or as an alternative, the issues described abovemay be addressed by a method for operating an engine with at least onerich cylinder and at least one lean cylinder, where the at least onerich cylinder is fueled via port fuel injection (PFI) and the at leastone lean cylinder is fueled via direct injection. By fueling the atleast one rich cylinder via PFI and the at least one lean cylinder viaDI, components may be prevented from overheating while improving enginetorque output performance.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an embodiment of a cylinder that may be included in anengine system according to at least one example of the presentdisclosure.

FIG. 2 shows a schematic depiction of a first example of an enginesystem.

FIG. 3 shows a schematic depiction of a second example of an enginesystem.

FIG. 4 shows a schematic depiction of a third example of an enginesystem.

FIG. 5 shows a flow chart of an operational method according to at leastone example of the present disclosure.

FIG. 6 shows a schematic depiction illustrating an example air fuelratio (AFR) effect on torque generation.

FIG. 7 shows a schematic depiction of example spark timing and torqueoutput at various air-fuel ratios.

FIG. 8A shows a schematic illustration of a first rolling split lambdaschedule according to at least one example of the present disclosure.

FIG. 8B shows a schematic illustration of a second rolling split lambdaschedule according to at least one example of the present disclosure.

FIG. 8C shows a schematic illustration of a third rolling split lambdaschedule according to at least one example of the present disclosure.

FIG. 8D shows a schematic illustration of a fourth rolling split lambdaschedule according to at least one example of the present disclosure.

FIG. 9A shows a schematic illustration of a first default split lambdaschedule according to at least one example of the present disclosure.

FIG. 9B shows a schematic illustration of a second default split lambdaschedule according to at least one example of the present disclosure.

FIG. 9C shows a schematic illustration of a third default split lambdaschedule according to at least one example of the present disclosure.

FIG. 9D shows a schematic illustration of a fourth default split lambdaschedule according to at least one example of the present disclosure.

FIG. 10A shows an example speed-load-operating mode map, according to atleast one example of the present disclosure.

FIG. 10B shows an example timeline for adjusting engine operation totransition between various operating modes, including a stoichiometricmode, a rolling split lambda mode, and a default split lambda modetaking into account the speed-load-operating mode map of FIG. 10A.

DETAILED DESCRIPTION

The following description relates to systems and methods for operating avehicle engine with split lambda fueling. In at least one example, thevehicle systems described herein may include one or more of theconfigurations as described at FIGS. 1-4. In at least one example, theapproach described herein may include operating the vehicle engine inaccordance with one or more of the strategies as described at FIG. 5 andat FIGS. 10A-10B. That is, the approach described herein may includetransitioning the vehicle engine operation between a stoichiometricmode, a default split lambda mode, and a rolling split lambda mode.Transitioning between the stoichiometric mode, default split lambdamode, and rolling split lambda mode first includes operating in thestoichiometric mode, so long as the stoichiometric mode does not resultin exhaust temperatures greater than a threshold. Otherwise, ifoperating in the stoichiometric mode results in the exhaust temperaturesbeing greater than the threshold, the engine is operated in one of thesplit lambda modes, which include the default split lambda mode and therolling split lambda mode.

If the engine is to be operated in the split lambda mode, the methodincludes determining whether to operate in the default split lambda modeor the rolling split lambda mode, depending on which split lambda mode(default or rolling) is better for NVH and exhaust temperaturereduction. For example, predictive calculations may be carried out topredict the impact of operating in the default split lambda mode and therolling split lambda mode on NVH and exhaust temperature, and the idealsplit lambda mode for exhaust temperature reduction and avoiding NVHwhile still achieving torque demands may be selected. That is, vehicleengine operation may be transitioned between various modes based onimpacts of operating the engine in that mode on one or more of NVH,exhaust temperature, and engine torque. In at least one example,evaluating whether or not operation in one of the engine modes will leadto NVH may be based at least in part on a resonant frequency condition,the resonant frequency condition based on a speed and load of theengine. That is, each of the operating modes may have a separateresonant frequency region of a speed-load map of the engine at whichgreater than a threshold amount of NVH occurs. Thus, selection andoperation of the engine in one of the stoichiometric mode, default splitlambda mode, and rolling split lambda mode may take into account theengine speed and load conditions, in at least one example.

It is noted that reference to an engine cycle herein refers to onecomplete engine cycle, where a single combustion of each of thecylinders of the engine has occurred. In the rolling split lambda mode,a plurality of engine cycles are carried out, with at least one enginecycle being a rich engine cycle and at least one engine cycle being alean engine cycle of the plurality of engine cycles. These rich and leanengine cycles beneficially help to reduce NVH by allowing fuelingschedules that avoid exciting the engine resonant frequency. Asexplained at least at FIGS. 8A-8D, a fuel schedule of the plurality ofengine cycles in the rolling split lambda mode still averages to besubstantially stoichiometric, so that substantially stoichiometricconditions are maintained at an emission control device downstream ofthe engine cylinders over the plurality of engine cycles. It is notedthat substantially stoichiometric refers an air-fuel-ratio beingsubstantially near a lambda value of 1.0. For example, substantiallystoichiometric may include lambda values between 0.95 to 1.05. Therolling split lambda mode is in contrast with the default split lambdamode. Whereas the rolling split lambda mode includes engine cycles whichare non-stoichiometric, each engine cycle in the default split lambdamode is operated to achieve stoichiometry, as discussed at FIGS. 9A-9D.Moreover, as described at FIG. 5 and at FIGS. 10A-10B, carrying out thedefault split lambda mode and the rolling split lambda mode may includefueling the rich cylinders with PFI and the lean cylinders with DI, inat least one example. By fueling the rich cylinders with PFI and thelean cylinders with DI, advantageous cooling effects may be achievedwhile maintaining engine torque output performance.

As further described at FIG. 5 and FIGS. 10A-10B, transitioning theengine operation between stoichiometric, default split lambda, androlling split lambda modes may include calculating a torque output ofthe engine based on one or more torque modifiers. These torque outputcalculations may include individually calculating the torque output ofeach cylinder or virtually grouping the cylinders into a rich cylindergroup and a lean cylinder group to perform the calculations. Asdiscussed at FIG. 6 and at FIG. 7, spark timing adjustments and air-fuelratio adjustments are two types of torque modifiers that impact a torqueoutput of the cylinders. By taking into account these torque modifiersin the manner as described at FIG. 5, increased accuracy and efficiencyin calculating the torque output may result.

Turning now to the figures, FIG. 1 shows a partial view of a singlecylinder 130 of an internal combustion engine 10 that may be included ina vehicle 5. Internal combustion engine 10 may be a multi-cylinderengine, and different engine system configurations for engine 10 will bedescribed below with respect to FIGS. 2-4. Cylinder (e.g., combustionchamber) 130 includes a coolant sleeve 114 and cylinder walls 132, witha piston 136 positioned therein and connected to a crankshaft 140.Combustion chamber 130 is shown communicating with an intake manifold 44via an intake valve 4 and an intake port 22 and with an exhaust port 86via exhaust valve 8.

In the depicted view, intake valve 4 and exhaust valve 8 are located atan upper region of combustion chamber 130. Intake valve 4 and exhaustvalve 8 may be controlled by a controller 12 using respective camactuation systems including one or more cams. The cam actuation systemsmay utilize one or more of cam profile switching (CPS), variable camtiming (VCT), variable valve timing (VVT), and/or variable valve lift(VVL) systems to vary valve operation. In the depicted example, intakevalve 4 is controlled by an intake cam 151, and exhaust valve 8 iscontrolled by an exhaust cam 153. The intake cam 151 may be actuated viaan intake valve timing actuator 101 and the exhaust cam 153 may beactuated via an exhaust valve timing actuator 103 according to setintake and exhaust valve timings, respectively. In some examples, theintake valves and exhaust valves may be deactivated via the intake valvetiming actuator 101 and exhaust valve timing actuator 103, respectively.For example, the controller may send a signal to the exhaust valvetiming actuator 103 to deactivate exhaust valve 8 such that it remainsclosed and does not open at its set timing. The position of intake cam151 and exhaust cam 153 may be determined by camshaft position sensors155 and 157, respectively.

In some examples, the intake and/or exhaust valve may be controlled byelectric valve actuation. For example, cylinder 130 may alternativelyinclude an intake valve controlled via electric valve actuation and anexhaust valve controlled via cam actuation, including CPS and/or VCTsystems. In still other examples, the intake and exhaust valves may becontrolled by a common valve actuator or actuation system or a variablevalve timing actuator or actuation system. Cylinder 130 can have acompression ratio, which is a ratio of volumes when piston 136 is atbottom dead center to top dead center. Conventionally, the compressionratio is in a range of 9:1 to 10:1. However, in some examples wheredifferent fuels are used, the compression ratio may be increased. Thismay happen, for example, when higher octane fuels or fuels with higherlatent enthalpy of vaporization are used. The compression ratio may alsobe increased if direct injection is used due to its effect on engineknock.

In some examples, each cylinder of engine 10 may include a spark plug 92for initiating combustion. An ignition system 88 can provide an ignitionspark to combustion chamber 130 via spark plug 92 in response to a sparkadvance signal SA from controller 12, under select operating modes.However, in some examples, spark plug 92 may be omitted, such as whereengine 10 initiates combustion by auto-ignition or by injection of fuel,such as when engine 10 is a diesel engine.

As a non-limiting example, cylinder 130 is shown including fuel injector66. Fuel injector 66 is a direct injector that is shown coupled directlyto combustion chamber 130 for injecting fuel directly therein inproportion to a pulse-width of a signal FPW received from controller 12via an electronic driver 168. In this manner, fuel injector 66 provideswhat is known as direct injection (hereafter also referred to as “DI”)of fuel into cylinder 130. While FIG. 1 shows injector 66 positioned tothe side, it may also be located overhead of the piston, such as nearthe position of spark plug 92. Such a position may increase mixing andcombustion when operating the engine with an alcohol-based fuel due tothe lower volatility of some alcohol-based fuels. Alternatively, theinjector may be located overhead and near the intake valve to helpimprove mixing. Further, in at least one example, each cylinder ofengine 10 may further include a port fuel injector 67 that provides fuelinto the intake port upstream of cylinder 130.

Fuel may be delivered to fuel injector 66 and port fuel injector 67 froma high pressure fuel system 180 including one or more fuel tanks, fuelpumps, and a fuel rail. Alternatively, fuel may be delivered by a singlestage fuel pump at a lower pressure. Further, while not shown, the fueltanks may include a pressure transducer providing a signal to controller12. Fuel tanks in fuel system 180 may hold fuel with different fuelqualities, such as different fuel compositions. These differences mayinclude different alcohol content, different octane, different heats ofvaporization, different fuel blends, and/or combinations thereof, etc.In some examples, fuel system 180 may be coupled to a fuel vaporrecovery system including a canister for storing refueling and diurnalfuel vapors. The fuel vapors may be purged from the canister to theengine cylinders during engine operation when purge conditions are met.

Engine 10 may be controlled at least partially by controller 12 and byinput from a vehicle operator 113 via an accelerator pedal 116 and anaccelerator pedal position sensor 118 and via a brake pedal 117 and abrake pedal position sensor 119. The accelerator pedal position sensor118 may send a pedal position signal (PP) to controller 12 correspondingto a position of accelerator pedal 116, and the brake pedal positionsensor 119 may send a brake pedal position (BPP) signal to controller 12corresponding to a position of brake pedal 117. Controller 12 is shownin FIG. 1 as a microcomputer, including a microprocessor unit 102,input/output ports 104, an electronic storage medium for executableprograms and calibration values shown as a read only memory 106 in thisparticular example, random access memory 108, keep alive memory 110, anda data bus. Storage medium read-only memory 106 can be programmed withcomputer readable data representing instructions executable bymicroprocessor 102 for performing the methods and routines describedherein as well as other variants that are anticipated but notspecifically listed.

Controller 12 may receive various signals from sensors coupled to engine10, in addition to those signals previously discussed, including ameasurement of inducted mass air flow (MAF) from mass air flow sensor48, an engine coolant temperature signal (ECT) from a temperature sensor112 coupled to coolant sleeve 114, a profile ignition pickup signal(PIP) from a Hall effect sensor 120 (or other type) coupled tocrankshaft 140, a throttle position (TP) from a throttle position sensorcoupled to a throttle 62, and an absolute manifold pressure signal (MAP)from a MAP sensor 122 coupled to intake manifold 44. An engine speedsignal, RPM, may be generated by controller 12 from signal PIP. Themanifold pressure signal MAP from the manifold pressure sensor may beused to provide an indication of vacuum or pressure in the intakemanifold.

Based on input from one or more of the above-mentioned sensors,controller 12 may adjust one or more actuators, such as fuel injector66, throttle 62, spark plug 92, the intake/exhaust valves and cams, etc.The controller may receive input data from the various sensors, processthe input data, and trigger the actuators in response to the processedinput data based on instruction or code programmed therein correspondingto one or more routines, an example of which is described with respectto FIG. 5.

In some examples, vehicle 5 may be a hybrid vehicle with multiplesources of torque available to one or more vehicle wheels 160. In otherexamples, vehicle 5 is a conventional vehicle with only an engine. Inthe example shown in FIG. 1, the vehicle includes engine 10 and anelectric machine 161. Electric machine 161 may be a motor or amotor/generator and thus may also be referred to herein as an electricmotor. Electric machine 161 receives electrical power from a tractionbattery 170 to provide torque to vehicle wheels 160. Electric machine161 may also be operated as a generator to provide electrical power tocharge battery 170, for example, during a braking operation.

Crankshaft 140 of engine 10 and electric machine 161 are connected via atransmission 167 to vehicle wheels 160 when one or more clutches 166 areengaged. In the depicted example, a first clutch 166 is provided betweencrankshaft 140 and electric machine 161, and a second clutch 166 isprovided between electric machine 161 and transmission 167. Controller12 may send a signal to an actuator of each clutch 166 to engage ordisengage the clutch, so as to connect or disconnect crankshaft 140 fromelectric machine 161 and the components connected thereto, and/orconnect or disconnect electric machine 161 from transmission 167 and thecomponents connected thereto. Transmission 167 may be a gearbox, aplanetary gear system, or another type of transmission. The powertrainmay be configured in various manners including as a parallel, a series,or a series-parallel hybrid vehicle. Electric machine 161 receiveselectrical power from a battery 170 to provide torque to vehicle wheels160. Electric machine 161 may also be operated as a generator to provideelectrical power to charge battery 170, for example during a brakingoperation.

As mentioned above, FIG. 1 shows only one cylinder of multi-cylinderengine 10. Referring now to FIG. 2, a schematic diagram of a firstexample engine system 200 is shown, which may be included in thepropulsion system of vehicle 5 of FIG. 1. For example, engine system 200provides a first example engine configuration of engine 10 introduced inFIG. 1. As such, components previously introduced in FIG. 1 arerepresented with the same reference numbers and are not re-introduced.In the example shown in FIG. 2, engine 10 includes cylinders 13, 14, 15,and 18, arranged in an inline-4 configuration, although otherconfigurations of engine 10 will be described with respect to FIGS. 3and 4. The engine cylinders may be capped on the top by a cylinder head.With respect to FIG. 2, cylinders 14 and 15 are referred to herein asthe inner (or inside) cylinders, and cylinders 13 and 18 are referred toherein as the outer (or outside) cylinders. The cylinders shown in FIG.2 may each have a cylinder configuration, such as the cylinderconfiguration described above with respect to FIG. 1.

Each of cylinders 13, 14, 15, and 18 includes at least one intake valve4 and at least one exhaust valve 8. The intake and exhaust valves may bereferred to herein as cylinder intake valves and cylinder exhaustvalves, respectively. As explained above with reference to FIG. 1, atiming (e.g., opening timing, closing timing, opening duration, etc.) ofeach intake valve 4 and each exhaust valve 8 may be controlled viavarious valve timing systems.

Each cylinder receives intake air (or a mixture of intake air andrecirculated exhaust gas, as will be elaborated below) from intakemanifold 44 via an air intake passage 28. Intake manifold 44 is coupledto the cylinders via intake ports (e.g., runners) 22. In this way, eachcylinder intake port can selectively communicate with the cylinder it iscoupled to via a corresponding intake valve 4. Each intake port maysupply air, recirculated exhaust gas, and/or fuel to the cylinder it iscoupled to for combustion.

As described above with respect to FIG. 1, a high pressure fuel systemmay be used to generate fuel pressures at the fuel injector 66 and,where included, the port fuel injector 67, coupled to each cylinder. Forexample, controller 12 may inject fuel into each cylinder at a differenttiming such that fuel is delivered to each cylinder at an appropriatetime in an engine cycle. As used herein, “engine cycle” refers to aperiod during which each engine cylinder fires once in a designatedcylinder firing order. A distributorless ignition system may provide anignition spark to cylinders 13, 14, 15, and 18 via the correspondingspark plug 92 in response to the signal SA from controller 12 toinitiate combustion. A timing of the ignition spark may be individuallyoptimized for each cylinder, as will be further described below withrespect to FIG. 5.

Inside cylinders 14 and 15 are each coupled to one exhaust port (e.g.,runner) 86 and outside cylinders 13 and 18 are each coupled to anexhaust port 87 for channeling combustion exhaust gases to an exhaustsystem 84. Each exhaust port 86 and 87 can selectively communicate withthe cylinder it is coupled to via the corresponding exhaust valve 8.Specifically, as shown in FIG. 2, cylinders 14 and 15 channel exhaustgases to a first exhaust manifold 81 via exhaust ports 86, and cylinders13 and 18 channel exhaust gases to a second exhaust manifold 85 viaexhaust ports 87. First exhaust manifold 81 and second exhaust manifold85 do not directly communicate with one another (e.g., no passagedirectly couples the two exhaust manifolds to one another).

Engine system 200 further includes a turbocharger 164, including aturbine 165 and an intake compressor 162 coupled on a common shaft (notshown). In the example shown in FIG. 2, turbine 165 is a twin scroll (ordual volute) turbine. In such an example, a first, hotter scroll of thetwin scroll turbine may be coupled to second exhaust manifold 85, and asecond, cooler scroll of the twin scroll turbine may be coupled to firstexhaust manifold 81 such that first exhaust manifold 81 and secondexhaust manifold 85 remain separated up to the turbine wheel. Forexample, the two scrolls may each introduce gas around the entireperimeter of the wheel, but at different axial locations. Alternatively,the two scrolls may each introduce gas to the turbine over a portion ofthe perimeter, such as over approximately 180 degrees of the perimeter.In another example, engine 10 may include a monoscroll turbine. In someexamples of the monoscroll turbine, first exhaust manifold 81 and secondexhaust manifold 85 may combine prior to reaching the turbine wheel viaa junction 202 as illustrated in FIG. 2. That is, the junction 202connects the first exhaust manifold 81 and the second exhaust manifold85 such that they converge. Thus, exhaust from the first exhaustmanifold 81 and the second exhaust manifold 85 is mixed and directeddownstream of junction 202 to turbine 165 via a singular passage 204.Via such configurations where the first exhaust manifold 81 and thesecond exhaust manifold 85 combine upstream of the turbine 165 as shownin FIG. 2, advantages as to reduced emissions may be achieved due toimproved exhaust mixing. Temperature control advantages may further beachieved. Such conjoining of the first exhaust manifold 81 and thesecond exhaust manifold 85 upstream of the turbine 165 may beparticularly advantageous to help consistent performance of the emissioncontrol device 70 when carrying out the varied fuel schedules of thestoichiometric, default split lambda, and rolling split lambda modesdescribed in further detail herein. The twin scroll configuration mayprovide greater power to the turbine wheel compared with the monoscrollconfiguration by providing a minimum volume (e.g., exhaust gas from twocylinders and a smaller manifold volume) from a given combustion event.In contrast, the monoscroll configuration enables use of lower costturbines that have higher temperature tolerances.

Rotation of turbine 165 drives rotation of compressor 162, disposedwithin intake passage 28. As such, the intake air becomes boosted (e.g.,pressurized) at the compressor 162 and travels downstream to intakemanifold 44. Exhaust gases exit turbine 165 into an exhaust passage 74.In some examples, a wastegate may be coupled across turbine 165 (notshown). Specifically, a wastegate valve may be included in a bypasscoupled between an inlet of turbine 165 and exhaust passage 74,downstream of an outlet of turbine 165. The wastegate valve may controlan amount of exhaust gas flowing through the bypass and to the outlet ofturbine. For example, as an opening of the wastegate valve increases, anamount of exhaust gas flowing through the bypass and not through turbine165 may increase, thereby decreasing an amount of power available fordriving turbine 165 and compressor 162. As another example, as theopening of the wastegate valve decreases, the amount of exhaust gasflowing through the bypass decreases, thereby increasing the amount ofpower available for driving turbine 165 and compressor 162. In this way,a position of the wastegate valve may control an amount of boostprovided by turbocharger 164. In other examples, turbine 165 may be avariable geometry turbine (VGT) including adjustable vanes to change aneffective aspect ratio of turbine 165 as engine operating conditionschange to provide a desired boost pressure. Thus, increasing the speedof turbocharger 164, such as by further closing the wastegate valve oradjusting turbine vanes, may increase the amount of boost provided, anddecreasing the speed of turbocharger 164, such as by further opening thewastegate valve or adjusting the turbine vanes, may decrease the amountof boost provided.

After exiting turbine 165, exhaust gases flow downstream in exhaustpassage 74 to an emission control device 70. Emission control device 70may include one or more emission control devices, such as one or morecatalyst bricks and/or one or more particulate filters. For example,emission control device may 70 include a three-way catalyst configuredto chemically reduce nitrogen oxides (NOx) and oxidize carbon monoxide(CO) and hydrocarbons (HC). In some examples, emission control device 70may additionally or alternatively include a gasoline particulate filter(GPF). After passing through emission control device 70, exhaust gasesmay be directed out to a tailpipe. As an example, the three-way catalystmay be maximally effective at treating exhaust gas with a stoichiometricair-fuel ratio (AFR), as will be elaborated below.

Exhaust passage 74 further includes a plurality of exhaust sensors inelectronic communication with controller 12, which is included in acontrol system 17. As shown in FIG. 2, exhaust passage 74 includes afirst oxygen sensor 90 positioned upstream of emission control device70. First oxygen sensor 90 may be configured to measure an oxygencontent of exhaust gas entering emission control device 70. Exhaustpassage 74 may include one or more additional oxygen sensors positionedalong exhaust passage 74, such as a second oxygen sensor 91 positioneddownstream of emission control device 70. As such, second oxygen sensor91 may be configured to measure the oxygen content of the exhaust gasexiting emission control device 70. In one example, one or more ofoxygen sensor 90 and oxygen sensor 91 may be universal exhaust gasoxygen (UEGO) sensors. Alternatively, a two-state exhaust gas oxygensensor may be substituted for at least one of oxygen sensors 90 and 91.Exhaust passage 74 may include various other sensors, such as one ormore temperature and/or pressure sensors. For example, as shown in FIG.2, a sensor 96 is positioned within exhaust passage 74 upstream ofemission control device 70. Sensor 96 may be a pressure and/ortemperature sensor. As such, sensor 96 may be configured to measure thepressure and/or temperature of exhaust gas entering emission controldevice 70.

Second exhaust manifold 85 is directly coupled to an exhaust gasrecirculation (EGR) passage 50 included in an EGR system 56. EGR passage50 is coupled between second exhaust manifold 85 and intake passage 28,downstream of compressor 162. As such, exhaust gases are directed fromsecond exhaust manifold 85 (and not first exhaust manifold 81) to airintake passage 28, downstream of compressor 162, via EGR passage 50,which provides high-pressure EGR. However, in other examples, EGRpassage 50 may be coupled to intake passage 28 upstream of compressor162.

As shown in FIG. 2, EGR passage 50 may include an EGR cooler 52configured to cool exhaust gases flowing from second exhaust manifold 85to intake passage 28 and may further include an EGR valve 54 disposedtherein. Controller 12 is configured to actuate and adjust a position ofEGR valve 54 in order to control a flow rate and/or amount of exhaustgases flowing through EGR passage 50. When EGR valve 54 is in a closed(e.g., fully closed) position, no exhaust gases may flow from secondexhaust manifold 85 to intake passage 28. When EGR valve 54 is in anopen position (e.g., from partially open to fully open), exhaust gasesmay flow from second exhaust manifold 85 to intake passage 28.Controller 12 may adjust the EGR valve 54 into a plurality of positionsbetween fully open and fully closed. In other examples, controller 12may only adjust EGR valve 54 to be either fully open or fully closed.Further, in some examples, a pressure sensor 34 may be arranged in EGRpassage 50 upstream of EGR valve 54.

As shown in FIG. 2, EGR passage 50 is coupled to intake passage 28downstream of a charge air cooler (CAC) 40. CAC 40 is configured to coolintake air as it passes through CAC 40. In an alternative example, EGRpassage 50 may be coupled to intake passage 28 upstream of CAC 40 (anddownstream of compressor 162). In some such examples, EGR cooler 52 maynot be included in EGR passage 50, as CAC cooler 40 may cool both theintake air and recirculated exhaust gases. EGR passage 50 may furtherinclude an oxygen sensor 36 disposed therein and configured to measurean oxygen content of exhaust gases flowing through EGR passage 50 fromsecond exhaust manifold 85. In some examples, EGR passage 50 may includeadditional sensors, such as temperature and/or humidity sensors, todetermine a composition and/or quality of the exhaust gas beingrecirculated to intake passage 28 from second exhaust manifold 85.

Intake passage 28 further includes throttle 62. As shown in FIG. 2,throttle 62 is positioned downstream of CAC 40 and downstream of whereEGR passage 50 couples to intake passage 28 (e.g., downstream of ajunction between EGR passage 50 and intake passage 28). A position of athrottle plate 64 of throttle 62 may be adjusted by controller 12 via athrottle actuator (not shown) communicatively coupled to controller 12.By modulating throttle 62 while operating compressor 162, a desiredamount of fresh air and/or recirculated exhaust gas may be delivered tothe engine cylinders at a boosted pressure via intake manifold 44.

To reduce compressor surge, at least a portion of the air chargecompressed by compressor 162 may be recirculated to the compressorinlet. A compressor recirculation passage 41 may be provided forrecirculating compressed air from a compressor outlet, upstream of CAC40, to a compressor inlet. A compressor recirculation valve (CRV) 42 maybe provided for adjusting an amount of flow recirculated to thecompressor inlet. In one example, CRV 42 may be actuated open via acommand from controller 12 in response to actual or expected compressorsurge conditions.

Intake passage 28 may include one or more additional sensors (such asadditional pressure, temperature, flow rate, and/or oxygen sensors). Forexample, as shown in FIG. 2, intake passage 28 includes MAF sensor 48disposed upstream of compressor 162 in intake passage 28. An intakepressure and/or temperature sensor 31 is also positioned in intakepassage 28 upstream of compressor 162. An intake oxygen sensor 35 may belocated in intake passage 28 downstream of compressor 162 and upstreamof CAC 40. An additional intake pressure sensor 37 may be positioned inintake passage 28 downstream of CAC 40 and upstream of throttle 62(e.g., a throttle inlet pressure sensor). In some examples, as shown inFIG. 2, an additional intake oxygen sensor 39 may be positioned inintake passage 28 between CAC 40 and throttle 62, downstream of thejunction between EGR passage 50 and intake passage 28. Further, MAPsensor 122 and an intake manifold temperature sensor 123 are shownpositioned within intake manifold 44, upstream of the engine cylinders.

Engine 10 may be controlled at least partially by control system 17,including controller 12, and by input from the vehicle operator (asdescribed above with respect to FIG. 1). Control system 17 is shownreceiving information from a plurality of sensors 16 (various examplesof which are described herein) and sending control signals to aplurality of actuators 83. As one example, sensors 16 may include thepressure, temperature, and oxygen sensors located within intake passage28, intake manifold 44, exhaust passage 74, and EGR passage 50, asdescribed above. Other sensors may include a throttle inlet temperaturesensor for estimating a throttle air temperature (TCT) coupled upstreamof throttle 62 in the intake passage. In at least one example, one ofthe sensors 16 may include one or more vibrational sensors. Such one ormore vibrational sensors may be positioned throughout engine 10 in orderto detect driveline NVH. Further, it should be noted that engine 10 mayinclude all or only a portion of the sensors shown in FIG. 2. As anotherexample, actuators 83 may include fuel injectors 66, port fuel injectors67, throttle 62, CRV 42, EGR valve 54, and spark plugs 92. Actuators 83may further include various camshaft timing actuators coupled to thecylinder intake and exhaust valves (as described above with reference toFIG. 1). Controller 12 may receive input data from the various sensors,process the input data, and trigger the actuators in response to theprocessed input data based on instruction or code programmed in a memoryof controller 12 corresponding to one or more routines. An examplecontrol routine (e.g., method) is described herein at FIG. 5.

The configuration of engine system 200 may enable engine performanceenhancement while reducing vehicle emissions. In particular, byincluding separate exhaust manifolds that do not directly communicateand that receive exhaust gases from different cylinders, the gasesreceived by first exhaust manifold 81 may have a different AFR than thegases received by second exhaust manifold 85. Herein, the AFR will bediscussed as a relative AFR, defined as a ratio of an actual AFR of agiven mixture to stoichiometry and represented by lambda (λ). A lambdavalue of 1 occurs during stoichiometric operation (e.g., atstoichiometry), wherein the air-fuel mixture produces a completecombustion reaction. A rich feed (λ<1) results from air-fuel mixtureswith more fuel relative to stoichiometry. For example, when a cylinderis enriched, more fuel is supplied to the cylinder via fuel injector 66and/or port fuel injector 67 than for producing a complete combustionreaction with an amount of air in the cylinder, resulting in excess,unreacted fuel. In contrast, a lean feed (λ>1) results from air-fuelmixtures with less fuel relative to stoichiometry. For example, when acylinder is enleaned, less fuel is delivered to the cylinder via fuelinjector 66 and/or port fuel injector 67 than for producing a completecombustion reaction with the amount of air in the cylinder, resulting inexcess, unreacted air. During nominal engine operation, the AFR mayfluctuate about stoichiometry, such as by λ generally remaining within2% of stoichiometry. For example, the engine may transition from rich tolean and from lean to rich between injection cycles, resulting in an“average” operation at stoichiometry.

Further, during some engine operating conditions, the AFR may bedeviated from stoichiometry. As one example, global enrichment (in whicheach cylinder is operated with a rich AFR) is a conventional performanceenhancement strategy to increase engine power. Generally, highercylinder air charges result in more engine torque and thus more enginepower, with the cylinder fueling correspondingly increased based on thehigher air charge to maintain the enrichment. In particular, theadditional, unreacted fuel cools engine system components, including thedownstream turbine 165 and emission control device 70, enabling more airflow for increased power while reducing heat-related degradation to thedownstream components (versus operating at stoichiometry with the highercylinder air charge). However, as mentioned above, emission controldevice 70 is most effective at stoichiometry, and thus, the abovedescribed global enrichment strategy results in increased vehicleemissions, particularly increased CO and HC emissions.

Therefore, according to the present disclosure, such as when high enginetorque (or high engine power) is demanded, a first set of cylinders maybe operated at a first, rich AFR, and a second, remaining set of theengine cylinders may be operated at a second, lean AFR. Such operationwill be referred to herein as “split lambda” operation (or operation ina split lambda mode). It is noted that both the default split lambdamode and the rolling split lambda mode described herein are examples ofsplit lambda operation. In particular, the inside cylinders may beoperated at the lean AFR, resulting cylinders 14 and 15 feeding leanexhaust gas to first exhaust manifold 81, and the outside cylinders maybe operated at the rich AFR, resulting in cylinders 13 and 18 feedingrich exhaust gas to second exhaust manifold 85. The lean exhaust gas infirst exhaust manifold 81 may be isolated from the rich exhaust gas insecond exhaust manifold 85 prior to mixing at and downstream of turbine165. Further, a degree of enleanment of the second set of cylinders mayselected based on a degree of enrichment of the first set of cylindersso that the exhaust gas from the first set of cylinders may mix with theexhaust gas from the second set of cylinders to form a stoichiometricmixture, even while none of the cylinders are operated at stoichiometry.Further still, the degree of enrichment of the first set of cylinders(and the degree of enleanment of the second set of cylinders) is greaterthan the typical fluctuation about stoichiometry performed duringnominal engine operation. As an example, the first set of cylinders maybe operated at a rich AFR having a lambda value in a range from 0.95-0.8(e.g., 5-20% rich).

By maintaining engine 10 at overall (e.g., global) stoichiometry, evenwhile operating in the split lambda operating mode, tailpipe emissionsmay be reduced. For example, operating in the split lambda mode mayresult in a substantial reduction in CO emissions compared toconventional enriched engine operation (e.g., a 90% reduction) whileproviding increased engine cooling and increased engine power, similarto the conventional enriched engine operation. As an example, controller12 may transition engine 10 to and from the split lambda operating moderesponsive to an increased engine demand, as will be further describedwith respect to FIG. 5.

Further, because EGR passage 50 is coupled to second exhaust manifold85, which receives the enriched exhaust gas from outside cylinders 13and 18 in during the split lambda operation, the exhaust gasrecirculated to intake passage 28 (and supplied to every cylinder ofengine 10) may be enriched. The enriched EGR contains relatively highconcentrations (or amounts) of CO and hydrogen gas compared with leanEGR and stoichiometric EGR. CO and hydrogen gas have high effectiveoctane numbers, offsetting the knock limit of each cylinder and creatingan opportunity for additional spark advance to both the enriched andenleaned cylinders. The spark advance provides additional temperaturerelief to turbine 165 and emission control device 70, enabling even moreair flow (and thus engine power) than when engine 10 is operated withoutenriched EGR. Thus, the cooled, enriched EGR may provide additionalknock and efficiency benefits to engine 10. Further still, even prior tooperating in the split lambda mode and enriching the EGR, providing EGRat high engine loads may provide engine cooling, enabling engine airflow to be increased relative to when no EGR is provided.

Other engine system configurations may also enable operation in thesplit lambda mode with enriched EGR for increased engine power andreduced emissions. Next, FIG. 3 shows a second example configuration ofengine 10. Specifically, FIG. 3 shows an example engine system 300 withengine 10 including cylinders 13, 14, 15, 19, 20, and 21 in a V-6configuration. However, other numbers of engine cylinders are alsopossible, such as a V-8 configuration. Except for the differencesdescribed below, engine system 300 may be substantially identical toengine system 200 of FIG. 2. As such, components previously introducedin FIGS. 1 and 2 are represented with the same reference numbers and arenot re-introduced.

In the example of engine system 300, engine 10 includes two enginebanks, first engine bank 312 and second engine bank 314. Specifically,first engine bank 312 includes cylinders 13, 14, and 15, each coupled tointake manifold 44 via intake ports 22, and second engine bank 314includes cylinders 19, 20, and 21, each coupled to intake manifold 44via intake ports 22. Each of cylinders 13, 14, and 15 of first enginebank 312 exhausts combustion gases to first exhaust manifold 81 viaexhaust ports 86. From first exhaust manifold 81, the gases may bedirected to a turbine 175 of a turbocharger 174. In contrast, each ofcylinders 19, 20, and 21 of second engine bank 314 exhausts combustiongases to second exhaust manifold 85, which is separate from exhaustmanifold 85, via exhaust ports 87. For example, no passages directlycouple first exhaust manifold 81 and second exhaust manifold 85. Fromsecond exhaust manifold 85, the gases may be directed to turbine 165 ofturbocharger 164, which is different than turbocharger 174. For example,turbine 175 is positioned in a first exhaust passage 77 and receivesexhaust gases exclusively from first exhaust manifold 81 for driving acompressor 172 positioned in an intake passage 29. Turbine 165 ispositioned in a second exhaust passage 76 and receives exhaust gasesexclusively from exhaust manifold 85 for driving compressor 162positioned in intake passage 28. For example, as shown, compressor 172may be coupled in parallel with compressor 162.

Thus, in the example configuration of engine system 300, exhaust system84 includes two separate exhaust manifolds, first exhaust manifold 81and second exhaust manifold 85, each coupled to engine cylinders of asingle engine bank. Further, exhaust system 84 includes twoturbochargers, turbocharger 164 and turbocharger 174, each having aturbine positioned to receive exhaust gas from only one of the twoexhaust manifolds.

First exhaust passage 77 and second exhaust passage 76 merge and arecoupled to exhaust passage 74 downstream of turbines 175 and 165,respectively. Exhaust passage 74 serves as a common exhaust passage. Insome examples, one or both of exhaust passages 77 and 76 may include aclose-coupled catalyst downstream of the corresponding turbine andupstream of exhaust passage 74. In the example shown in FIG. 3, a firstclose-coupled catalyst 78 is optionally positioned in first exhaustpassage 77 downstream of turbine 175 and upstream of where first exhaustpassage 77 couples with common exhaust passage 74, and a secondclose-coupled catalyst 72 is optionally positioned in second exhaustpassage 76 downstream of turbine 165 and upstream of where secondexhaust passage 76 couples with common exhaust passage 74. In contrast,emission control device 70 is positioned in common exhaust passage 74.Thus, while first close-coupled catalyst 78 receives exhaust gasexclusively from first engine bank 312 (e.g., via first exhaust manifold81 and turbine 175) and second close-coupled catalyst 72 receivesexhaust gas exclusively from second engine bank 314 (e.g., via secondexhaust manifold 85 and turbine 165), emission control device 70receives exhaust gas from both first engine bank 312 and second enginebank 314, and all of the exhaust gas directed out the tailpipe passesthrough exhaust passage 74 and emission control device 70. However, inother examples, first close-coupled catalyst 78 and/or secondclose-coupled catalyst 72 may be omitted.

When first close-coupled catalyst 78 and second close-coupled catalyst72 are included, they may reduce vehicle emissions prior to operating inthe split lambda mode (e.g., during an engine cold start). For example,due to being positioned closer to engine 10, first close-coupledcatalyst 78 and second close-coupled catalyst 72 may receive more heatfrom the engine than emission control device 70 and may thereforeachieve light-off faster. However, first close-coupled catalyst 78 andsecond close-coupled catalyst 72 may be less efficient while operatingin the split lambda mode due to receiving only rich or lean exhaust gas.In such examples, emission control device 70 may effectively treatexhaust gas components not treated by first close-coupled catalyst 78and second close-coupled catalyst 72.

As shown in FIG. 3, exhaust passage 74 includes first oxygen sensor 90and sensor 96, each positioned upstream of emission control device 70,and the optional second oxygen sensor 91, positioned downstream ofemission control device 70, as in engine system 200 described above withrespect to FIG. 2. In other examples, additionally or alternatively,exhaust gas sensors, such as oxygen, temperature and/or pressuresensors, may be coupled to first exhaust passage 77 and/or secondexhaust passage 76. For example, an oxygen sensor may be coupled tofirst exhaust passage 77 upstream of first close-coupled catalyst 78and/or coupled to second exhaust passage 76 upstream of secondclose-coupled catalyst 72.

Intake passages 28 and 29 may be configured as two parallel intakepassages that merge and couple to a common intake passage 30 upstream ofthrottle 62. As shown in FIG. 3, intake passage 28 includes CAC 40, asintroduced in FIG. 2, and intake passage 29 includes a second CAC 43.However, in other examples, a single charge air cooler may be included,such as positioned in common intake passage 30 upstream of throttle 62.Intake passage 29 may include a second set of some or all of the varioussensors positioned in intake passage 28 and described above with respectto FIG. 2 for determining various qualities of the intake air beingprovided to engine 10. For example, intake passage 29 is shown includinga MAF sensor 49, a temperature sensor 32, and an intake oxygen sensor33. Alternatively, only one of intake passages 28 and 29 may includeeach sensor. For example, intake passage 28 may include MAF sensor 48and temperature sensor 31 (and not intake oxygen sensor 35), and intakepassage 29 may include intake oxygen sensor 33 (and not MAF sensor 49and temperature sensor 32). As another example, intake passage 29 mayinclude MAF sensor 49 (and not temperature sensor 32 and intake oxygensensor 33), and intake passage 28 may include temperature sensor 31 andintake oxygen sensor 35 (and not MAF sensor 48).

Further, intake passage 29 may include a compressor recirculationpassage 46 for recirculating compressed air from an outlet of compressor172, upstream of CAC 43, to an inlet of compressor 172. A CRV 45 may beprovided for adjusting an amount of flow recirculated to the inlet ofcompressor 172. Thus, compressor recirculation passage 46 and CRV 45 mayfunction similarly to compressor recirculation passage 41 and CRV 42,respectively, as described above with respect to FIG. 2.

In the example of engine system 300, EGR passage 50 is directly coupledto second exhaust manifold 85 and is not coupled to first exhaustmanifold 81. Thus, EGR system 56 recirculates exhaust gases produced bycombustion in second engine bank 314 and not first engine bank 312 whenEGR valve 54 is at least partially open. Further EGR passage 50 is showncoupled to intake passage 28 downstream of CAC 40 and upstream of whereintake passage 28 couples to common intake passage 30. However, in otherexamples, EGR passage 50 may be coupled to common intake passage 30,such as upstream of throttle 62. Because intake passage 28 flows intakeair to common intake passage 30, which provides intake air to everycylinder of engine 10 via intake manifold 44, when EGR is requested, therecirculated exhaust gas may be provided to each cylinder of engine 10.

Due to the configuration of EGR system 56, the cylinders of secondengine bank 314 may be operated at the first, rich AFR, and thecylinders of first engine bank 312 may be operated at the second, leanAFR. In particular, cylinders 19, 20, and 21 may be operated at the richAFR, resulting in rich exhaust gas flowing to second exhaust manifold85, a portion of which may be recirculated to intake passage 28 via EGRpassage 50. Cylinders 13, 14, and 15 may be operated at the lean AFR,resulting in lean exhaust gas flowing to first exhaust manifold 81. Thelean exhaust gas in first exhaust manifold 81 is isolated from the richexhaust gas in second exhaust manifold 85 prior to mixing at exhaustpassage 74. Thus, while rich exhaust gas may flow through secondclose-coupled catalyst 72 and lean exhaust gas may flow through firstclose-coupled catalyst 78 during the split lambda operation, the exhaustgas flowing through emission control device 70 may be maintainedstoichiometry, on average, to decrease emissions.

Still other engine systems may be operated in the split lambda mode.Turning to FIG. 4, a third example configuration of engine 10 is shown.Specifically, FIG. 4 shows an example engine system 400, with engine 10having an inline-3 configuration instead of the inline-4 configurationof engine system 200 of FIG. 2. Except for the differences describedbelow, engine system 400 may be substantially identical to engine system200 of FIG. 2. As such, components previously introduced in FIGS. 1-3are represented with the same reference numbers and are notre-introduced.

As mentioned above, in the example of engine system 400, engine 10includes cylinders 13, 14, and 15, arranged in an inline-3configuration. Further, exhaust system 84 of engine system 300 includesonly exhaust manifold 85. As such, exhaust manifold 85 is coupled toeach of cylinders 13, 14, and 15 (e.g., every cylinder of engine 10) viaexhaust ports 87, and exhaust manifold 85 receives exhaust gasesexpelled from all of the cylinders of engine 10. The exhaust gasesreceived by exhaust manifold 85 may be channeled to turbine 165, asdescribed above.

When EGR is provided via EGR system 56, such as when EGR valve 54 is atleast partially open, a portion of the exhaust gas may flow through EGRpassage 50. In the example of engine system 300, EGR passage 50 mayreceive exhaust gas originating from each of cylinders 13, 14, and 15.However, EGR passage 50 is coupled to exhaust port 87 of cylinder 13,upstream of where exhaust port 87 of cylinder 13 joins exhaust manifold85. Due to the position of EGR passage 50 of exhaust port 87 and fluiddynamics within exhaust manifold 85, a much higher proportion of theexhaust gas recirculated through EGR passage 50 may originate fromcombustion within cylinder 13 compared with cylinders 14 and 15. Forexample, at least 80% of the exhaust gas flowing through EGR passage 50may originate from combustion within cylinder 13. However, in otherexamples the EGR passage 50 may simply be coupled to exhaust manifold85.

Due to the odd number of cylinders in engine 10 in engine system 400,operation in the split lambda mode may be different than when the enginehas an even number of cylinders (such as in engine system 200 of FIG. 2and engine system 300 of FIG. 3). For example, cylinders 13, 14, and 15each may be operated with a different AFR while the exhaust gas thatflows from exhaust manifold 85 to emission control device 70 maintainsglobal stoichiometry. That is, a first cylinder may be operated at afirst, rich AFR, a second cylinder may be operated at a second,stoichiometric AFR, and a third, remaining cylinder may be operated at athird, lean AFR, resulting in a stoichiometric mixture upstream ofemission control device 70.

Thus, the systems of FIGS. 2-4 provide three example engineconfigurations (e.g., an inline configuration having an even number ofcylinders, a V-configuration, and an inline configuration having an oddnumber of cylinders) and descriptions of how each of the three engineconfigurations enables operation in the split lambda mode with enrichedEGR, thereby increasing engine power while decreasing fuel usage andreducing vehicle emissions. Note that the number of cylinders in eachconfiguration may be changed without parting from the scope of thisdisclosure.

Turning to FIG. 5, FIG. 5 provides an example engine operation method500, including operation in a default split lambda mode and a rollingsplit lambda mode. For example, the default split lambda combustionstrategy inherently causes an imbalance between rich and lean cylindersdue to different burn rates, which may result in engine vibrations.Therefore, method 500 provides a control strategy for mitigating thisimbalance in order to reduce the engine vibrations, including a torquecalculation approach. Moreover, during conditions in which the engine isoperating in a region where a default split lambda fueling scheduleexcites the engine resonant frequency, method 500 includes a controlstrategy for transitioning into a rolling split lambda mode, duringwhich a fueling schedule is altered to prevent issues of NVH.Instructions for carrying out method 500 and the rest of the methodsincluded herein may be executed by a controller (e.g., controller 12 ofFIGS. 1-4) based on instructions stored on a memory of the controllerand in conjunction with signals received from sensors of the enginesystem, such as the sensors described above with reference to FIGS. 1-4.The controller may employ engine actuators of the engine system (e.g.,fuel injectors 66, 67 of FIGS. 1-4, spark plug 92 of FIGS. 1-4, andthrottle valve 62 of FIGS. 1-4) to adjust engine operation according tothe methods described below. Moreover, it is noted that reference to anemission control device at FIGS. 5-10 may refer to an emission controldevice such as emission control device 70 shown in FIGS. 1-4.

At 502, method 500 includes estimating and/or measuring engine operatingconditions. The operating conditions may include, for example, athrottle position, brake pedal position, an accelerator pedal position,ambient temperature and humidity, barometric pressure, engine speed,engine load, engine torque, engine temperature, mass air flow (MAF),intake manifold pressure (MAP), a commanded AFR, an actual AFR ofexhaust gas entering an emission control device (e.g., emission controldevice 70 of FIGS. 2-4), an exhaust temperature, etc.

As an example, the controller may use the accelerator pedal position todetermine the engine torque demanded by a vehicle operator. For example,the controller may input the accelerator pedal position and the enginespeed into an engine map to determine the engine torque demand. Further,the controller may determine engine power produced based on the enginetorque and the engine speed, such as by multiplying the engine torque bythe engine speed. As another example, the controller may determine aboost pressure provided by a turbocharger (e.g., turbocharger 164 ofFIGS. 2-4) based on (e.g., as a function of) MAP and the barometricpressure. Furthermore, as discussed later herein, the controller mayinput the engine speed and the engine load into an engine map todetermine whether the engine is operating in a default split lambda modeor a rolling split lambda mode is optimal for reducing NVH and exhausttemperature.

As part of estimating and measuring engine operating conditions at step502, the controller may estimate a torque output of the cylinders,taking into account torque modifiers. These torque modifiers may includeone or more of an AFR, spark timing as a distance from maximum braketorque (MBT) timing, and EGR. For example, the controller may refer toone or more look-up tables which include information as to the AFR andspark timing effects on torque output. These look-up tables may includeinformation such as provided in FIG. 6 and FIG. 7, in at least oneexample. In at least one example, such look-up tables may be stored onboard in memory of the controller. Additionally or alternatively, theselook-up tables may be stored remotely as part of a cloud storage system,and these look-up tables may be accessed by the controller by way of awireless connection. In one or more examples, it is noted that FIGS. 6and 7 may be integrated into the torque modifiers to include in eitherreal-time or predictive torque output calculations. Discussion as toapproaches for performing torque output calculations, including thedetermination of torque output modifiers, is included in further detailbelow.

Turning briefly to FIG. 6 and FIG. 7, FIG. 6 and FIG. 7 illustrate someof the effects of such torque modifiers. In particular, FIG. 6 shows aschematic depiction 600 illustrating an example AFR effect on torquegeneration 602, where spark timing is kept constant. As shown in FIG. 6,602 shows the torque at the y-axis is plotted as a function of AFR atthe x-axis. The torque at the y-axis increases with a direction of they-axis arrow, and the AFR at the x-axis increases with a direction ofthe x-axis arrow from a rich AFR to a lean AFR.

As may be seen in FIG. 6, torque generation 602 generally increases froma lean AFR to a stoichiometric AFR 604, with the torque generation 602being approximately the same at the stoichiometric AFR 604 as when theAFR is only slightly lean. When operating only slightly rich of thestoichiometric AFR 604, torque generation 602 is approximately the sameas at the stoichiometric AFR 604. As the AFR becomes increasingly rich,however, the torque generation 602 increases, then plateaus, and theneventually decreases.

Turning to FIG. 7, FIG. 7 shows a schematic depiction 700 illustratingexample spark timing and torque output at various air-fuel ratios(AFRs), including a rich AFR 702, stoichiometric AFR 704, and a lean AFR706. As illustrated at FIG. 7, torque generation is plotted as afunction of spark timing. The torque generation is represented by they-axis and increases in a direction of the y-axis arrow. The sparktiming is represented by the x-axis, with a degree of advancementincreasing in a direction of the x-axis arrow. Further, MBT spark timingis shown at 708. As may be seen in FIG. 7, moving from retarded sparktiming to MBT 708, torque generation increases for each of the rich AFR702, stoichiometric AFR 704, and lean AFR 706. However, a rate ofincrease in torque generation when adjusting the spark timing fromretarded spark timing to MBT 708 differs for each of the rich AFR 702,stoichiometric AFR 704, and lean AFR 706. In particular, adjusting thespark timing from retarded spark timing to MBT 708 increases torquegeneration of the lean AFR 706 at a higher rate than both the rich AFR702 and the stoichiometric AFR 704. Further, adjusting the spark timingfrom retarded spark timing to MBT 708 increases torque generation of therich AFR 702 at a lower rate than both the lean AFR 706 and thestoichiometric AFR 704. When the spark timing is at approximately MBT708, the torque generation for each of the rich AFR 702, stoichiometricAFR 704, and lean AFR 706 peaks and plateaus.

Thus, only slightly retarding or slightly advancing the spark timingrelative to MBT 708 does not significantly impact an amount of torquegeneration for any of the AFRs. The range of spark timing where torquegeneration peaks occurs is different for each of the rich AFR 702,stoichiometric AFR 704, and lean AFR 706. The rich AFR 702 has thelargest spark timing range for torque generation peak, followed by thestoichiometric AFR 704, and the lean AFR 706 has the smallest torquegeneration plateau.

Looking now to advancing the spark timing relative to MBT 708, torquegeneration for each of the rich AFR 702, stoichiometric AFR 704, andlean AFR 706 plateaus and then decreases when advancing the spark timingrelative to MBT 708. Moreover, similar to adjusting spark timing fromretarded to MBT 708, adjusting spark timing from MBT 708 to advancedimpacts torque generation of the various AFRs at different rates.

In particular, adjusting the spark timing from MBT 708 to advanced sparktiming decreases torque generation of the lean AFR 706 at a higher ratethan both the rich AFR 702 and the stoichiometric AFR 704. Further,adjusting the spark timing from MBT 708 to advanced spark timingdecreases torque generation of the rich AFR 702 at a lower rate thanboth the lean AFR 706 and the stoichiometric AFR 704.

Turning back to step 502 of FIG. 5, as a part of the estimating and/ormeasuring the engine operating conditions, method 500 may includecarrying out torque output calculations at step 503. The torquecalculations at step 503 may be used to estimate engine torque, comparethe engine torque to a driver demand, determine whether the estimatedengine torque matches the driver demand, and adjust correspondingactuators accordingly (e.g., throttle, wastegate, cams, fueling, etc.),in at least one example. Additionally or alternatively, the torquecalculations at step 503 may be used in a predictive manner as describedlater under scenario analysis.

It is noted that cylinders using PFI as compared to DI fueling may havedifferent trapped masses, which affects the cylinder torque. As such,PFI as compared to DI fueling may impact knock and therefore spark,which is accounted for in the spark modifier discussed below.

In a first approach, the torque output calculations at step 503 mayinclude calculating the torque output for each cylinder separately andthen summing the torque outputs together as follows:Tq_(cyl,0)=TqMod_(cyl)(engspeed,load,VCT)×Tq_(engine)(engspeed,load,VCT)/N_(cyl)Tq_(cyl)=Tq_(cyl,0)×TqMod_(AFR)(λ_(cyl))×TqMod_(spk)(SpkRetMBT_(cyl))×TqMod_(DI)(fDI_(cyl))×TqMod_(EGR)Tq_(total)=Σ_(all cylinders)Tq_(cyl)

For reference, Tq_(cyl,0) is a cylinder torque for stoichiometric, withMBT, and no EGR operation. Tq_(cyl) is the torque output of anindividual cylinder, which may be either a lean cylinder or a richcylinder. TqMod_(cyl) is a modifier to account for variation in cylinderbreathing (that is, cylinder intake and exhaust). Such variation may bebased on one or more of a VCT of the particular cylinder and a positionof the cylinder in the cylinder arrangement. TqMod_(spk) may be a torquemodifier based on spark using a function or a look-up table (such as a1-D table). The TqMod_(spk) looked up in such a table may either be aTqMod_(spk) (SpkRetMBT_(cyl)) if the spark timing is retarded from MBTor a TqMod_(spk) (SpkAdvMBT_(cyl)) if the spark timing is advanced fromMBT for a particular cylinder. The look-up table for an advanced orretarded TqMod_(spk) may include information, such as shown at FIG. 7.Moreover, the TqMod_(spk) may take into account the knock limits of anindividual cylinder and thus vary from cylinder to cylinder to avoidsuch knock limits. Such knock limits of an individual cylinder may bebased on one or more of the breathing characteristics and the amount ofrich or lean bias of the cylinder, in one or more examples.

It is noted that while the above equation reflects SpkRetMBT_(cyl) forspark retard from MBT that the equation above may instead reflectSpkAdvMBT_(cyl) in a case where the spark timing of the individualcylinder being evaluated is advanced of MBT. In at least one example, adifferent value may be assigned to the lean cylinders compared to therich cylinders for TqMod_(spk), at least in part on an amount of rich orlean bias taking into account a function or look-up table such as theone shown at FIG. 6. Additionally, the SpkRetMBT_(cyl) orSpkAdvMBT_(cyl) spark timing may vary among each group due to individualcylinder knock control. TqMod_(AFR) may be a function or a look-up table(such as a 1-D table). For example, the TqMod_(AFR) may be based on afunction or look-up table such as shown at FIG. 6. λ_(cyl) represents arich λ value for rich cylinders and a lean λ value for lean cylinders.TqMod_(DI) is a modifier for DI fraction. For example, 0 or 0.1TqMod_(DI) may be assigned to rich cylinders, and 1 or 0.9 TqMod_(DI)may be assigned to the lean cylinders. TqMod_(EGR) is a value which maytake into account the impact of additional fuel from EGR. TheTqMod_(EGR) may be based on a function or a look-up table, in at leastone example.

It is noted that the torque modifiers may include AFR, spark timing as adistance from MBT (SpkRetMBT), DI fraction (fDI), and EGR. In this firstapproach, feed forward spark is calculated as a function of engine speedand load. Additionally, the torque modifiers (rich or lean) are appliedfor AFR, spark timing, and EGR, and these modifiers are applied toindividual cylinders depending on if that cylinder is a rich cylinder orlean cylinder. This first approach for performing torque calculations isparticularly advantageous for obtaining accurate torque estimates whenoperating the engine in the rolling split lambda mode. This is at leastdue in part to cylinder-to-cylinder variations in the AFR and the sparktiming which occur in the split lambda mode. Further, as the cylindersmay be varied in torque output from cylinder to cylinder in the rollingsplit lambda mode, performing torque output calculations for eachcylinder separately may be advantageous to monitor engine balancing.

By computing individual cylinder torques, cylinder-to-cylinder variationin breathing (air intake and exhaust) can advantageously be accountedfor. For example, these variations in cylinder breathing can be morepronounced on some engine configurations like a V8 with cross-planecrankshaft, where a positioning of the cylinder may vary the breathingcharacteristics of the cylinders.

Changing which set of cylinders is lean and which set is rich, even ifthe total number of rich and lean cylinders remained the same can resultin a different engine torque due to cylinder-to-cylinder variation inbreathing, in at least one example. Such variation may further be due tofuel puddling in at least one example. That is, in cases of PFI, fuelpuddling from the PFI may contribute to a cylinder-to-cylinder variancein torque output.

In the case of carrying out a rolling split lambda mode, these sets oflean cylinders and rich cylinders will be changing from cycle to cycle.Thus, it may be particularly advantageous to follow the first approachfor calculating a total torque output of the engine (Tq_(total)) asdescribed above, where the torque output of the cylinders isindividually calculated and then summed (Σ_(all cylinders)Tq_(cyl))while carrying out the rolling split lambda mode.

Further, some cylinders may be more prone to knock than others, and thusindividual knock control will adjust the spark accordingly. Computingindividual cylinder torques and then summing the individual cylindertorques advantageously allows to account for the impact of individualcylinder spark retard.

In at least one example, it is noted that the torque output of theengine may be based on current engine operating conditions using outputsof one or more sensors of the engine for the calculations describedabove in the first approach. In other examples, however, a predictivetorque output of the engine may instead be predictive values generatedby a controller of the engine and used as part of a scenario analysis inthe first approach.

In addition to the above first approach for performing toque outputcalculations, the torque output calculations that account for torquemodifiers may further be carried out via a second approach where leanand rich cylinders are grouped together as a virtual bank of cylindersfor calculation purposes. Via the second approach, feed forward spark iscalculated as a function of engine speed and load. Additionally,modifiers (rich or lean) are applied for AFR and EGR, and applied to therich and lean banks of cylinders depending on if the cylinders in thebank are rich or lean cylinders. It is noted that the banks of cylindersmay also be referred to as groups of cylinders herein. Via the secondapproach, the torque may be calculated as follows:Tq_(cylinder,average)=Tq_(engine)(engspeed,load,VCT)/N _(cylinders)Tq_(lean group)=Tq_(cylinder,average) ×N _(lean cylinders)×TqMod_(lean)Tq_(rich group)=Tq_(cylinder,average) ×N _(rich cylinders)×TqMod_(rich)Tq_(total)=Tq_(lean group)+Tq_(rich group)

Grouping the cylinders for performing torque estimations may achieve thetechnical effect of calculation efficiency and a reduced computing loadon the controller compared to other approaches which do not carry outsuch grouping.

In the example second approach shown above, an average cylinder torqueoutput (Tq_(cylinder,average)) for all of the plurality of cylinders ofthe engine is calculated based on a torque output of the engine(Tq_(engine)) divided by a total number of the plurality of cylinders ofthe engine (N_(cylinders)). The average cylinder torque output(Tq_(cylinder,average)) is based on stoichiometric operating conditions,in at least one example. The torque output of the engine takes intoaccount an engine speed (engspeed), engine load (load), and variable camtiming (VCT) of the engine. In at least one example, it is noted thatthe torque output of the engine may be based on current engine operatingconditions using outputs of one or more sensors of the engine. In otherexamples, however, a predictive torque output of the engine may insteadbe predictive values generated by a controller of the engine and used aspart of a scenario analysis.

Continuing with the second approach, a torque output of a lean group ofcylinders (Tq_(lean group)) of the engine is calculated, and a torqueoutput of the rich group of cylinders (Tq_(rich group)) is calculated.The lean group of cylinders comprises all enleaned cylinders of theplurality of cylinders. The rich group of cylinders comprises allenriched cylinders of the plurality of cylinders. It is noted that anamount of rich bias for each of the enriched cylinders may be same inthe second approach. Further, the amount of lean bias for each of theenleaned cylinders may be the same in the second approach.

To calculate the torque output of the lean group of cylinders, the totalnumber of lean cylinders in the lean cylinder group (N_(lean cylinders))is multiplied by the average cylinder torque output(Tq_(cylinder,average)) and is multiplied by a lean torque modifier(TqMod_(lean)). The lean torque modifier (TqMod_(lean)) may be apredetermined modifier to adjust the average cylinder torque output(Tq_(cylinder,average)) based on the amount of lean bias. For example,the lean torque modifier (TqMod_(lean)) may be based on the AFR of thelean cylinders of the engine and reference to a function or a look-uptable containing data such as is shown at FIG. 6.

To calculate the torque output of the rich group of cylinders, the totalnumber of rich cylinders in the lean cylinder group (N_(rich cylinders))is multiplied by the average cylinder torque output(Tq_(cylinder,average)) and is multiplied by a rich torque modifier(TqMod_(rich)). The rich torque modifier (TqMod_(rich)) may be apredetermined modifier to adjust the average cylinder torque output(Tq_(cylinder,average)) based on the amount of rich bias. For example,the rich torque modifier (TqMod_(rich)) may be based on the AFR of therich cylinders of the engine and reference to a function or look-uptable containing data such as is shown at FIG. 6.

The total toque output of the engine may then be calculated by addingthe calculated lean cylinder group torque output (Tq_(lean group)) andthe calculated rich cylinder group torque output (Tq_(rich group)).

These torque output calculations may be used for determining a currentengine torque output in addition to or as an alternative to varioussensor outputs (e.g., a profile ignition pickup signal (PIP) from a Halleffect sensor 120 (or other type) coupled to crankshaft 140). Forexample, these torque output calculations may be used to makeadjustments to evaluate torque output in real-time, making adjustmentsfor one or more of air-fuel-ratios of the engine cylinders, a positionof an EGR valve, and spark timing.

In at least one example, these output torque calculations may be carriedout for each engine cycle so that the controller is updated with themost recent engine operating conditions. However, in some examples,these output torque calculations may be carried out for a subset of theengine cycles during vehicle operation.

As mentioned above, the torque output calculations above may be used aspredictive calculations by the controller to calculate the rolling splitlambda fueling schedules and the default split lambda fueling schedulesdiscussed below (e.g., at steps 512, 514, 518, 520).

Further, in at least one example, the torque output calculations mayadditionally take into account whether port fuel injection or directinjection is being used as a further torque modifier. For example, incases where port fuel injection is used for the rich cylinders anddirect injection is used for the lean cylinders, the torque outputcalculations above may be adjusted by a multiplier. This multiplier mayincrease the torque output calculations by approximately 5% to 7% in atleast one example.

Moving to step 504, based on the estimated and/or measured engineoperating conditions at step 502, method 500 includes determiningwhether the torque demand is greater than a threshold torque demand. Inone or more examples, the threshold torque demand may be a function ofengine speed. The threshold torque demand may be a pre-calibratednon-zero engine torque value above which the torque cannot be furtherincreased while operating the engine at stoichiometry without riskingheat-related degradation to exhaust system components, such as a turbineof the turbocharger (e.g., turbine 165 of FIGS. 2-4) and the emissioncontrol device. As mentioned above with respect to FIG. 2, more engineair flow (e.g., higher MAF and/or MAP values) results in more enginepower. However, as also mentioned above, this increases the temperatureof the exhaust gas produced, and thus, the temperature of the exhaustsystem components. Therefore, the threshold torque demand may be setbased on a threshold exhaust temperature, the threshold exhausttemperature including a pre-calibrated non-zero exhaust temperaturevalue above which exhaust system component degradation may be increased.As an alternative example of the method at 504, it may be determined ifthe engine power demand is greater than a first threshold power, whichmay correspond to the threshold torque demand at a given engine speed.

If the torque demand is not greater than the threshold torque demand(“NO”), method 500 proceeds to 506 and includes operating the engine ina stoichiometric mode (also referred to herein as a stoichiometricoperating mode). In at least one example, it is noted that the torqueoutput calculations at step 503 may be compared to the torque demandreceived at step 502. Then, based on a difference between the torqueoutput calculations at step 503 compared to the torque demand receivedat step 502, a fueling schedule for the stoichiometric mode may beselected and/or created and associated actions may be carried out toachieve the torque demand (e.g., adjusting VCT, actuating fuelinjectors, adjusting actuation of spark plugs for spark timingadjustments, adjusting a position of an EGR valve, adjusting a positionof an intake throttle, etc.). During operation in the stoichiometricmode, all cylinders of the engine may be operated at a stoichiometricAFR for all engine cycles. Boost may be provided via the turbochargerbased on the torque demand. However, boost pressure (e.g., amount ofboost) may be limited based on the exhaust temperature, such as tomaintain the exhaust temperature below the threshold exhausttemperature. Thus, the boost pressure may be kept below atemperature-limited boost pressure threshold while operating in thestoichiometric mode. As one example, the temperature-limited boostpressure threshold may correspond to the boost pressure for producingthe threshold torque demand. During stoichiometric operation, dualinjection may be carried out. In at least one example, a minimum pulsewidth (or minimum PFI fraction and DI fraction) may be required for eachDI and PFI injector to avoid deposit build-ups, for purposes of fuelrail temperature control, and for purposes of fuel injector tiptemperature control. For example, at least 10% PFI or 10% DI may need tobe maintained.

Additionally or alternatively, in at least one example, there may be achoice between carrying out PFI, DI, or a combination of both PFI and DIbased on one or more of predicted emissions, knock, engine componenttemperatures, exhaust gas temperatures, and torque output, for example.For example, a selection between carrying out PFI, DI, or a combinationof both PFI and DI may be based on which option is predicted to bestreduce one or more of emission and knock.

Following step 506, method 500 may then end. Further, method 500 may berepeated so that the controller may update the operating mode asoperating conditions change. For example, the controller mayautomatically and continuously (e.g., in real-time) repeat at leastparts of method 500 so that changes in operating conditions, suchchanges in the torque demand, may be detected based on signals receivedfrom sensors of the engine system and evaluated to determine if thechange in operating conditions warrant a change in the engine operatingmode.

Returning to 504, if instead the torque demand is greater than thethreshold torque demand (“YES”), method 500 proceeds to 508 where it isdetermined whether dual fuel injection is available. In particular,method 500 includes determining whether both direct injection (DI) andport fuel injection (PFI) is available at step 508.

In some examples, dual fuel injection may only be determined asavailable (“YES”) if all of the cylinders have both DI and PFIavailability. However, in other examples, dual fuel injection may bedetermined on a cylinder by cylinder basis. Thus, in one or moreexamples, dual fuel injection is determined to be available (“YES”) aslong as at least one of the cylinders has both DI and PFI availability.Put another way, in at least one example, dual fuel injection may bedetermined to be available (“YES”) responsive to only a subset of thecylinders having dual fuel injection available at step 508. In at leastone example, an availability for dual fuel injection may includeperforming a diagnostic to determine whether each of the directinjectors (e.g., direct injectors 66) and the each of the port fuelinjectors (e.g., port fuel injectors 67) are functional. For example,the direct injectors may be commanded to inject an amount of fuel intothe cylinders as part of the diagnostic, and a flow meter may bemonitored to determine whether the commanded amount of fuel was injectedvia the direct injectors. Additionally or alternatively, theavailability of dual fuel injection may include determining anavailability of fuel for each of the direct injectors and port fuelinjectors, as a fuel source for each of the direct injectors and theport fuel injectors may be separate in some configurations. For example,the availability of fuel may be based on a fuel level sensor positionedwithin a direct injector fuel source and based on a fuel level sensorpositioned in a port fuel injector fuel source. In at least one example,the direct injectors may be the direct injectors 66 and the port fuelinjectors may be the port fuel injectors 67, as illustrated at FIGS.1-4.

Should both DI and PFI be available at step 508, then it is determinedthat dual fuel injection is available (“YES”) at step 508, and method508 proceeds to step 510.

At step 510, method 500 includes determining whether or not the enginesatisfies rolling split lambda conditions. That is, step 510 includesdetermining whether the engine is being operated in rolling split lambdaconditions. Such rolling split lambda conditions may refer to engineoperating conditions (such as speed and load) where the rolling splitlambda mode is estimated to achieve less than a threshold NVH and lessthan a threshold exhaust temperature. The rolling split lambdaconditions may be a set of engine operating conditions at which therolling split lambda mode is calculated to result in NVH less than thethreshold NVH and/or reduced exhaust temperatures (such as exhausttemperatures less than the threshold exhaust temperature) compared tooperating in the stoichiometric mode or the default split lambda mode.

Put another way, step 510 includes determining whether or not it isoptimal to operate the engine in rolling split lambda mode. Method 500may check if a rolling split lambda fueling schedule reduces NVHcompared to a default split lambda schedule. It is noted that such NVHis due at least in part to amplification of the fueling schedulefrequency (frequency of the shortest repeating pattern) from resonance.Method 500 may also check if a rolling split lambda fueling schedulereduces exhaust temperature compared to a default split lambda schedule.This is possible in cases where one fueling schedule may allow largerrich and lean biases.

In at least one example, calculating the NVH for operating in therolling split lambda mode may include comparing current speed loadconditions of the engine to an associated resonant frequency region forthe rolling split lambda mode on a speed-load map. The resonantfrequency region may also be referred to as a resonant frequencycondition, in at least one example. The resonant frequency region forthe rolling split lambda mode may correspond to engine operatingconditions at which NVH greater than an NVH threshold occurs if theengine is operated in the rolling split lambda mode, where the NVHthreshold is a non-zero value. Resonance occurs due to drivelinefrequency resonating with the engine frequency, in at least one example.

Thus, in one or more examples, the determination as to whether or not tooperate the engine in the rolling split lambda mode may be based on anengine speed and load. For example, the rolling split lambda mode maycorrespond to regions II, IV, VI, and VIII illustrated in speed-load map1000 at FIG. 10A.

As may be seen at FIG. 10A, at low RPM, maximum torque can be achievedwith stoichiometric mode (exhaust temperatures are below the acceptablethreshold). The load boundary 1028 at the upper boundary of region Icorresponds to the torque demand threshold 504 from method 500. Athigher RPMs, split lambda may be needed to reduce the temperature,however. As further discussed below, FIG. 10A only includes cases whererolling split lambda mode is used in an RPM range when the torque demandthreshold 504 is satisfied, cases where default split lambda mode isused in an RPM range when torque demand threshold 504 is satisfied, andcases where there is a switch between the rolling split lambda mode andthe default split lambda mode.

Determination as to whether rolling split lambda mode conditions arepresent may be based off of a look-up table which takes into accountengine speed and load as related to driveline frequency, as well asfrequencies associated with the rolling split lambda mode fuelingschedule and frequencies associated with the default split lambda modefueling schedule. It is noted that the rolling split lambda modeconditions are engine operating conditions (such as engine speed andload) in which operating in the rolling split lambda mode is determinedto be optimal compared to operation in the default split lambda mode andstoichiometric mode to reduce NVH, exhaust temperature, and emissions,while still achieving a desired torque output.

The look-up table may correspond to such split lambda fueling schedulefrequencies and a speed-load map, such as speed-load map 1000 at FIG.10A, in at least one example. In particular, an estimated/detectedengine speed and load may be used as inputs into the look-up table(e.g., inputs into a function of the look-up table) that may be accessedvia the controller of the engine system. Then, based on the output, thecontroller of the engine determines whether the speed and load inputsresult in operation in the stoichiometric mode, default split lambdamode or rolling split lambda mode. The engine speed and load conditionsas related to whether to operate in the rolling split lambda mode,default split lambda mode, or stoichiometric mode may be empiricallypredetermined and stored in the look-up table and correspondingspeed-load map. The engine speed and load conditions as related to therolling split lambda mode, default split lambda mode, and stoichiometricmay be used to determine an optimal fueling schedule for operating theengine, in at least one example. It is noted that operating in any ofthe rolling split lambda mode, default split lambda mode, andstoichiometric mode includes carrying out a fueling schedule associatedwith the rolling split lambda mode, default split lambda mode, andstoichiometric mode, respectively.

Responsive to determining to operate in the rolling split lambda mode(“YES”) at step 510, method 500 includes operating the engine in arolling split lambda mode at step 512. That is, the engine maysimultaneously benefit from operating in the rolling split lambda modewhile dual fuel injection is available in order for method 500 to carryout step 512.

In the rolling split lambda mode, a fueling schedule of the engine isaltered such that a plurality of individual non-stoichiometric enginecycles are carried out while maintaining substantially stoichiometricconditions at an emission control device (e.g., emission control device70). That is, the exhaust gas at the emission control device may besubstantially stoichiometric. In particular, in the rolling split lambdamode, the sum of the engine cycles for the fueling schedule isstoichiometric though the fueling schedule includes a plurality ofnon-stoichiometric engine cycles.

In order to determine the fueling schedule to use in the split lambdamode at step 512, torque output calculations as discussed above withregard to step 502 may be utilized to perform predictive calculations.For example, the torque output calculations discussed at step 502 may beused as predictive calculations to perform scenario analysis for variouscombinations of torque modifiers when in the rolling split lambda mode.

In examples where the torque output calculations may be used forpredictive purposes, various combinations of potential AFR and sparktiming values may be used in conjunction with the above-discussed torqueoutput calculations to perform a scenario analysis. In the case of therolling split lambda mode, the torque output calculations mayspecifically be carried out by calculating the torque output for eachcylinder separately and then summing the torque outputs together. Inthis way, factors such as engine balancing may be taken into accountwhen selecting the rolling split lambda fueling schedule.

By carrying out a plurality of non-stoichiometric engine cycles duringconditions where the engine is operating in a region where default splitlambda fueling schedule excites the engine resonant frequency at step510, the technical effect of mitigating amplification due to resonanceis achieved, and the NVH of the engine is advantageously reduced.Meanwhile, by maintaining overall substantially stoichiometricconditions at the emission control device for the predetermined numberof engine cycles, catalyst breakthrough may be avoided.

It is noted that catalyst breakthrough, also referred to as slip, is acondition during which emission control device (e.g., catalyst) activitydecreases to the point that NOx and hydrocarbons pass through theemission control device without conversion. Such a decrease in emissioncontrol device activity may be due to temperature conditions that areless than a threshold light-off temperature for a catalyst of theemission control device, as well as due to overloading of the emissioncontrol device when operating the engine with an overall rich AFR. Thelight-off temperature may be a temperature at which a catalyst operatesat 50% conversion, in at least one example.

Further, as dual fuel injection is available at step 512, port fuelinjection (PFI) is used for the rich cylinders and direct injection (DI)is used for lean cylinders of the engine during the rolling split lambdamode at step 512. For example, PFI may be carried out via one or more ofthe port fuel injectors 67, and DI may be carried out via one or more ofthe direct injectors 66. In cases where dual fuel injection isdetermined to be available at step 508 because all of the cylinders havedual fuel injection availability, all of the cylinders may be operatedwith PFI for the rich cylinders and DI for the lean cylinders. In caseswhere dual fuel injection is determined to be available at step 508because a portion of the cylinders has dual fuel injection availability(and not all of the cylinders have dual fuel injection), the portion ofthe cylinders with dual fuel injection availability is controlled withPFI when operated rich and DI when lean. The remaining cylinders whichdo not have dual fuel injection availability may be operated with eitheronly PFI or only DI (whichever is available).

PFI and DI may produce different torques based on which injectionsystems are being used. One reason for the torque difference is due tothe charge cooling effect produced by DI, which can produce 5%-7% moretorque. Such differences in torque production may be accounted for inthe predictive torque output calculations for the rolling split lambdamode at step 512.

In view of the above, by using PFI for the rich cylinders and DI for thelean cylinders at step 512, the lean cylinders will benefit from chargecooling and the torques produced by the lean cylinders will more closelymatch the torque produced by the rich cylinders. In turn, engine balancemay be achieved and NVH is avoided when using varied AFRs for thecylinders during an engine cycle.

Looking briefly to FIGS. 8A-8D, example rolling split lambda fuelingschedules are shown. It is noted that the fueling schedules disclosedherein (including the rolling split lambda fueling schedules) may notonly be directed towards commands for commanding a fuel injector andcontrolling a fueling injection amount. Rather, the fueling schedulesherein may encompass commands associated with various torque modifiers.For example, the fueling schedules herein may be used to adjust one ormore actuators, which in turn adjusts various torque modifiers. Forexample, one or more of the throttle, direct fuel injectors, port fuelinjectors, EGR valve, and spark plugs may adjusted based on the fuelingschedule to in turn adjust one or more torque modifiers. Such one ormore torque modifiers may include AFR and spark, for example. EGR mayadditionally be taken into account as a separate torque modifier, in atleast one example. However, EGR may alternatively be included in the AFRtorque modifier.

As to the rolling split lambda fueling schedules discussed at FIGS.8A-8D, these rolling split lambda fueling schedules may be selectedand/or created via the torque output calculations discussed at step 503.For example, the rolling split lambda fueling schedules may be selectedand/or created via the use of the torque output calculations discussedat step 503 to perform a scenario analysis for various torque outputmodifiers. In at least one example, it is noted that the torque outputcalculations at step 503 may be compared to the torque demand receivedat step 502. Then, based on a difference between the torque outputcalculations at step 503 compared to the torque demand received at step502, rolling split lambda fueling schedules may be selected and/orcreated and actions associated with the rolling split lambda fuelingschedules may be carried out (e.g., adjusting VCT, actuating fuelinjectors, adjusting actuation of spark plugs for spark timingadjustments, adjusting a position of an EGR valve, adjusting a positionof an intake throttle, etc.).

In the case of the rolling split lambda fueling schedules, the firstapproach discussed for torque output calculations (where individualcylinder torque outputs are calculated and then summed) may beadvantageous. However, it is also possible to utilize the secondapproach for calculating the torque output discussed at step 503, whichincludes grouping the rich and lean cylinders for the calculations.

In some examples, the scenario analysis may be used to evaluate aplurality of predetermined rolling split lambda fueling schedules andselect one of the predetermined rolling split lambda fueling schedules.Additionally or alternatively, the scenario analysis may be used tocreate custom rolling split lambda fueling schedules in real-time. Forexample, should none of the predetermined rolling split lambda fuelingschedules be acceptable based on one or more criteria, a custom rollingsplit lambda fueling schedule may be created in real-time via the torqueoutput calculations.

Performing the scenario analysis may include carrying out multipletorque output calculations with various combinations of potential torquemodifiers. For example, the torque output calculations for variouspotential combinations of spark timing and AFRs may be calculated. Insome examples, the torque output for the various combinations of sparktiming and AFRs may be evaluated at least in part by referencing alook-up table including AFR and spark timing data relative to torqueoutput, such as illustrated at FIGS. 6 and 7.

In at least one example, the scenario analysis may compile predictivedata for various combinations of spark timing and AFRs for each cylinderin an engine cycle for a series of multiple engine cycles. The scenarioanalysis may further include compiling predictive data for these variouscombinations of spark timing and AFRs for a series of multiple enginecycles. This predictive data may include one or more of an overallpredicted torque output for the engine, a predicted engine speed, apredicted torque output for each cylinder of the engine, a predictedexhaust AFR, and a predicted amount of catalyst loading for each of thespark timing and AFR combinations, for example.

Referencing the predictive data, selection of the rolling split lambdafueling schedule may then be carried out based on one or more criteria.For example, chosen AFRs and spark timings for the rolling split lambdafueling schedule may be to prevent excessive exhaust temperatures(exhaust temperatures exceeding a temperature threshold). Such excessiveexhaust temperatures may be caused by one or more of smaller rich andlean biases, and larger spark retards increase exhaust temperature.

Additionally or alternatively, the chosen AFRs of the rolling splitlambda fueling schedule using a rich-lean fueling pattern may avoidcatalyst breakthrough. It is noted that larger rich and lean biases, andlonger sequences of consecutive rich cylinders or consecutive leancylinders increase the risk of catalyst breakthrough.

Further, in at least one example, the chosen AFRs, spark timings, andrich-lean fueling pattern of the rolling split lambda fueling schedulemay result in acceptable NVH (NVH less than the NVH threshold).Different rich-lean fueling patterns have different frequencies, andfrequencies closer to resonant frequency increase NVH. Larger rich andlean biases lead to larger torque fluctuations between rich and leancylinders and potentially higher NVH. Assigning different spark timingsto rich and lean cylinders can increase or decrease a torque discrepancybetween rich and lean cylinders, leading to higher or lower NVH. Thus,the selection of the rolling split lambda fueling schedule may take intoaccount the impacts of the AFRs, spark timings, and rich-lean fuelingpattern on NVH.

Further still, the chosen AFRs and spark timings for the rolling splitlambda fueling schedule may be able to achieve the demanded torque.

Thus, the one or more criteria for selection of the rolling split lambdafueling schedule may include one or more of a demanded torque output, apredicted exhaust temperature, a catalyst breakthrough threshold, athreshold amount of torque modulation, an engine balancing threshold,estimated NVH, and a fuel efficiency. In at least one example, ifmultiple fueling schedules satisfy all the criteria, then the fuelingschedule with the lowest fuel consumption or lowest NVH may be chosen.

Turning first to FIG. 8A, a first rolling split lambda fueling schedule800 is shown. In the first rolling split lambda fueling schedule 800,rich cylinders 802 are denoted via the circles with hatching and leancylinders 804 are denoted via solid circles. The first rolling splitlambda fueling schedule 800 is a four engine cycle fueling schedule,including a first engine cycle 806, a second engine cycle 808, a thirdengine cycle 810, and a fourth engine cycle 812. Completion of eachfueling cycle for the first rolling split lambda fueling schedule 800thus includes one completion of each of the first engine cycle 806, thesecond engine cycle 808, the third engine cycle 810, and the fourthengine cycle 812. In at least one example, the engine cylinders shownmay be all of the cylinders of the engine. Alternatively, the enginecylinders shown may be one of two cylinder banks. Further, in theexample shown at FIG. 8A, four cylinders are shown, though other numbersof cylinders are possible. In at least one example, a firing order ofthe cylinders is maintained.

In the first example rolling split lambda fueling schedule 800, it isnoted that each of the rich cylinders 802 are operated at a percentagerich that is equal to a percentage lean of each of the lean cylinders804. By operating the rich cylinders 802 at a percentage rich equal tothe percentage lean of the lean cylinders 804, overall stoichiometry isachieved at the completion of each fueling cycle while modulating thetorque to avoid resonance issues.

Using PFI in comparison to DI may result in changes in the cylindertrapped mass which can affect the torque calculations. Operation in PFIor DI also can affect knock, which is accounted for in the torquecalculation through the spark modifier.

When using PFI for rich cylinders and DI for lean cylinders, asdiscussed in at least one example herein, some adjustments for transientfueling may be necessary to account for fuel puddling during rollingsplit lambda operation.

For example, consider a cylinder alternating rich and lean from cycle tocycle. In such a case, if PFI is scheduled for this cylinder every othercycle, fuel in the puddle has twice the time to evaporate betweeninjections (and part of the fuel that evaporated would go into the leancycle, so the DI amount calculations are adjusted to account for suchpuddling).

Furthermore, fueling schedules may result in some rich cycles beingpreceded by rich cycles or lean cycles (for the same cylinder), whichmay result in changes in the size of the fuel puddle among the richcycles. Fuel puddling is also accounted for when switching betweenstoichiometric mode and the split lambda mode, as the manifold pressuremay change. For example, one or more of fuel injection and VCT may beadjusted to compensate for such manifold pressure changes.

For example, each of the rich cylinders 802 may be operated at 20% rich(a phi value of 1.20) and each of the lean cylinders 804 may be operatedat 20% lean (a phi value of 0.80) where phi (φ)=1/lambda.

In other words, to maintain overall stoichiometry, the rich lambdashould be 0.83 and the lean lambda should be 1.25. The overall lambda ofmultiple cylinders (with equal mass flow rate) is not the average ofindividual cylinder lambda, therefore: λ=1+x and λ=1−x do not result ina stoichiometric mixture unless x (where x is the bias) is small.Instead, the overall phi of multiple cylinders is the average of theindividual cylinder phi: φ=1+x and φ=1−x result in a stoichiometricmixture.

Put another way, for exemplary purposes, consider a first cylinder withdoubled fueling (λ=0.5, φ=2), and a second cylinder with no fueling(λ=∞, φ=0). The overall λ and φ should both be 1, but averaging λ wouldresult in ∞.

Or, in another example, each of the rich cylinders 802 may be operatedat 15% rich (a phi value of 1.15) and each of the lean cylinders 804 maybe operated at 15% lean (a phi value of 0.85).

Further percentage amounts for rich and lean are possible withoutdeparting from the scope of this disclosure, so long as the percentageused for the rich cylinders 802 and the lean cylinders 804 is below anemission control device breakthrough percentage and achievesstoichiometry at the completion of each schedule. That is, theparticular percentage rich and percentage lean used in the operation ofthe cylinders for the first example rolling split lambda fuelingschedule 800 are selected such that completion of each fueling scheduleavoids emission control device breakthrough and achieves substantiallystoichiometric conditions at the emission control device.

In the first example rolling split lambda fueling schedule 800, thefirst engine cycle 806 and the second engine cycle 808 arestoichiometric, while the third engine cycle 810 and the fourth enginecycle 812 are non-stoichiometric. In particular, the third engine cycle810 is lean and the fourth engine cycle 812 is rich, where an amountthat third engine cycle 810 is enleaned is a same amount as the fourthengine cycle 812 is enriched. For example, if the third engine cycle 810results is an overall 20% lean engine cycle, then the fourth enginecycle 812 is an overall 20% rich engine cycle. In this way, after onecompletion of each of the first engine cycle 806, second engine cycle808, third engine cycle 810, and fourth engine cycle 812, the firstexample rolling split lambda fueling schedule 800 results insubstantially stoichiometric conditions at an emission control devicedownstream from the engine cylinders. Based on averages, however, it isnoted that the 20% rich and 20% lean cylinders example mentionedpreviously may result in engine cycle 810 being 10% lean (average of+20%, +20%, +20%, −20% lean) and engine cycle 812 being 10% rich(average of −20%, +20%, +20%, +20% rich). In one or more examples, anorder of the engine cycles in the first example rolling split lambdafueling schedule 800 may be altered. Moreover, which cylinders are richand which cylinders are lean within each engine cycle may be adjustedwithout departing from the scope of this disclosure. The inclusion ofthe non-stoichiometric cycles in the first example rolling split lambdafueling schedule 800 modulates the engine torque and is particularlyadvantageous to avoid resonance issues. That is, by modulating theengine torque, an amount of time that the engine is operated at speedswhich cause driveline resonance may be avoided to reduce overalldriveline NVH.

Turning to FIG. 8B, FIG. 8B shows a second example rolling split lambdafueling schedule 801. In the second rolling split lambda fuelingschedule 801, rich cylinders 814 are denoted via the circles withhatching and lean cylinders 816 are denoted via solid circles. The firstrolling split lambda fueling schedule 801 is a three engine cyclefueling schedule, including a first engine cycle 818, a second enginecycle 820, and a third engine cycle 822. Completion of each fuelingcycle for the second rolling split lambda fueling schedule 801 thusincludes one completion of each of the first engine cycle 818, thesecond engine cycle 820, and the third engine cycle 822. Further, in theexample shown at FIG. 8B, four cylinders are shown, though other numbersof cylinders are possible. In at least one example, a firing order ofthe cylinders is maintained.

In the second example rolling split lambda fueling schedule 801, it isnoted that each of the rich cylinders 814 are operated at a percentagerich that is twice a percentage lean of each of the lean cylinders 816.By operating the rich cylinders 814 at percentage rich twice thepercentage lean of the lean cylinders 816, overall stoichiometry isachieved at the completion of each fueling cycle while modulating thetorque to avoid resonance issues.

Further percentage amounts for rich and lean are possible withoutdeparting from the scope of this disclosure, so long as the percentageused for the rich cylinders 814 and the lean cylinders 816 is below anemission control device (e.g., catalyst) breakthrough percentage andachieves stoichiometry at the completion of each schedule. That is, theparticular percentage rich and percentage lean used in the operation ofthe cylinders for the second example rolling split lambda fuelingschedule 801 are selected such that completion of each fueling scheduleavoids emission control device breakthrough and achieves substantiallystoichiometric conditions at the emission control device uponcompletion. In at least one example, emission control devicebreakthrough may be referred to as catalyst breakthrough.

In the second example rolling split lambda fueling schedule 801, none ofthe engine cycles are stoichiometric. That is, each of the engine cyclesin the second example rolling split lambda fueling schedule 801 arenon-stoichiometric. In particular, the first engine cycle 818 is a richengine cycle. The second engine cycle 820 and the third engine cycle 822are lean engine cycles.

In a case where the rich engine cylinders 814 are operated at 20% rich(a phi value of 1.20) and the lean cylinders 816 are operated at 10%lean (a phi value of 0.90), the first engine cycle 818 may thus be 5%rich (an average of +20%, −10%, −10%, and +20% rich); the second enginecycle 820 2.5% lean; and the third engine cycle 822 2.5% lean.

In at least one example, engine cycles of the second example rollingsplit lambda fueling schedule 801 may be carried out in a differentorder. Further, the cylinders shown in the second example rolling lambdafueling schedule 801 may represent all of the cylinders of the engine.Or, alternatively, the cylinders shown in the second example rollingsplit lambda fueling schedule 801 may represent one of two cylinderbanks of the engine. In cases where the engine comprises two cylinderbanks, the second example rolling split lambda fueling schedule 801 maybe coordinated with the other cylinder bank to avoid emission controldevice breakthrough while still modulating the torque to avoid resonanceissues. In one or more examples, the first example rolling lambdafueling schedule may be used for a first cylinder bank and the secondexample rolling lambda fueling schedule may be used for a secondcylinder bank.

Turning to FIG. 8C, FIG. 8C shows a third example rolling split lambdafueling schedule 803. In the third rolling split lambda fueling schedule803, rich cylinders 824 are denoted via the circles with hatching andlean cylinders 826 are denoted via solid circles. The third rollingsplit lambda fueling schedule 803 is a four engine cycle fuelingschedule, including a first engine cycle 828, a second engine cycle 830,a third engine cycle 832, and a fourth engine cycle 834. Completion ofeach fueling cycle for the third rolling split lambda fueling schedule803 thus includes one completion of each of the first engine cycle 828,the second engine cycle 830, the third engine cycle 832, and the fourthengine cycle 834. Further, in the example shown at FIG. 8C, threecylinders are shown, though other numbers of cylinders are possible. Inat least one example, a firing order of the cylinders is maintained.

In the third example rolling split lambda fueling schedule 803, it isnoted that each of the rich cylinders 824 are operated at a percentagerich that is equal to a percentage lean of each of the lean cylinders826. This being the case, as there are an odd number of cylinders, eachof the first engine cycle 828, the second engine cycle 830, the thirdengine cycle 832, and the fourth engine cycle 834 of the third examplerolling split lambda fueling schedule 803 are non-stoichiometric enginecycles. However, in following the third example rolling split lambdafueling schedule, operating the rich cylinders 824 at a percentage richequal to the percentage lean of the lean cylinders 826, achievessubstantially stoichiometric conditions at the emission control deviceupon one completion of each of the first, second, third, and fourthengine cycles of the third example rolling split lambda fueling schedule803 while modulating the torque to avoid resonance issues.

For example, each of the rich cylinders 824 may be operated at 20% rich(a phi value of 1.20) and each of the lean cylinders 826 may be operatedat 20% lean (a phi value of 0.80). Or, in another example, each of therich cylinders 824 may be operated at 15% rich (a phi value of 1.15) andeach of the lean cylinders 826 may be operated at 15% lean (a phi valueof 0.85).

Further percentage amounts for rich and lean are possible withoutdeparting from the scope of this disclosure, so long as the percentageused for the rich cylinders 824 and the lean cylinders 826 is below anemission control device breakthrough percentage and achievesstoichiometry at the completion of each schedule. That is, theparticular percentage rich and percentage lean used in the operation ofthe cylinders for the third example rolling split lambda fuelingschedule 803 are selected such that completion of each fueling scheduleavoids emission control device breakthrough and achieves substantiallystoichiometric conditions at the emission control device.

As mentioned above, in the third example rolling split lambda fuelingschedule 803, none of the engine cycles are stoichiometric. Rather, allof the engine cycles are non-stoichiometric. In particular, the firstengine cycle 828 and the third engine cycle 832 are lean, and the secondengine cycle 830 and the fourth engine cycle 834 are rich. It is notedthat an amount the engine is enleaned is equal to an amount that theengine is enriched upon completion of the first engine cycle 828, secondengine cycle 830, third engine cycle 832, and fourth engine cycle 834.

In one or more examples, it is noted that lean to rich alternation maynot be cycle to cycle and that smaller portions of a cycle may bealternating. For example, to minimize the risk of catalyst breakthrough,a shortest alternating pattern, or shortest sequences of consecutiverich cylinders or consecutive lean cylinders available, may be selected.

For example, though the above-discussed sequence alternates rich andlean cycles, the above sequence results in four consecutive leancylinders and four consecutive rich cylinders. In at least one example,the schedule shown at FIG. 8C may instead carry out the fueling patternshown in a different order. That is, rather than third rolling splitlambda fueling schedule 803 carrying out the engine cycle fueling inorder of first engine cycle 828, second engine cycle 830, third enginecycle 832, and then fourth engine 834 as shown, the third rolling splitlambda fueling schedule may instead be carried out with a fueling orderof first engine cycle 828, second engine cycle 830, fourth engine cycle834, and then third engine cycle 832. By switching the order of thethird engine cycle 832 and the fourth engine cycle 834 fueling in thisway, the result is a fueling cycle that alternates rich and lean every 2cycles, and the longest sequence of consecutive rich or lean cylindersis reduced to three which may advantageously reduce catalystbreakthrough risk.

Further still, in at least one example, a better fueling cycle from acatalyst breakthrough standpoint may be to have the rich cylinders (R)and lean cylinders (L) as follows: [(RRL)-(LRR)-(LLR)-(RLL)]. It isnoted that each set of three cylinders in parentheses represents oneengine cycle and that the entire sequence is in brackets. Thus,[(RRL)-(LRR)-(LLR)-(RLL)] represents the rich and lean bias and order offour engine cycles. In following this sequence, fueling cycles alternaterich and lean every two cycles, and the longest sequence of consecutiverich or lean cylinders is reduced to two.

Continuing, an even further variation which achieves event furtheradvantages from a catalyst breakthrough standpoint is: [(RLR)-(LRL)]. Inthis way, the longest sequence of consecutive rich or lean cylinders isreduced to one. Nonetheless, even though this variation may be betterfrom a catalyst breakthrough standpoint, as has been discussedthroughout the disclosure, other factors such as NVH may impact thefinal selection of the fueling schedule. For example, the [(RLR)-(LRL)]sequence has double the frequency of [(RRL)-(LRR)-(LLR)-(RLL)]. Thus,one of [(RLR)-(LRL)] and [(RRL)-(LRR)-(LLR)-(RLL)] may be preferablefrom an NVH perspective. The preferred fueling cycle (based on NHV) mayvary with engine operating condition.

Moreover, which cylinders are rich and which cylinders are lean withineach engine cycle may be adjusted without departing from the scope ofthis disclosure. That is, in FIG. 8C, the first engine cycle 828 isshown with the far left cylinder as a rich cylinder 824. However, inother examples, the middle cylinder or the right cylinder may be therich cylinder 824.

Turning to FIG. 8D, FIG. 8D shows a fourth example rolling split lambdafueling schedule 805. In the fourth rolling split lambda fuelingschedule 805, rich cylinders 836 are denoted via the circles withhatching and lean cylinders 838 are denoted via solid circles. Thefourth rolling split lambda fueling schedule 805 is a four engine cyclefueling schedule, including a first engine cycle 840, a second enginecycle 842, a third engine cycle 844, and a fourth engine cycle 846.Completion of each fueling cycle for the fourth rolling split lambdafueling schedule 805 thus includes one completion of each of the firstengine cycle 840, the second engine cycle 842, the third engine cycle844, and the fourth engine cycle 846. Further, in the example shown atFIG. 8D, three cylinders are shown, though other numbers of cylindersare possible. In at least one example, a firing order of the cylindersis maintained.

In the fourth example rolling split lambda fueling schedule 805, it isnoted that each of the rich cylinders 836 are operated at a percentagerich that is twice a percentage lean of each of the lean cylinders 838.In following the fourth example rolling split lambda fueling schedule,operating the rich cylinders 836 at a percentage rich twice thepercentage lean of the lean cylinders 838, substantially stoichiometricconditions are achieved at the emission control device upon completionof each fueling cycle while modulating the torque to avoid NVH fromresonance issues.

For example, each of the rich cylinders 836 may be operated at 20% rich(a phi value of 1.20) and each of the lean cylinders 838 may be operatedat 10% lean (a phi value of 0.90). Further percentage amounts for richand lean are possible without departing from the scope of thisdisclosure, so long as the percentage used for the rich cylinders 836and the lean cylinders 838 is below an emission control devicebreakthrough percentage and achieves stoichiometry at the completion ofeach schedule. That is, the particular percentage rich and percentagelean used in the operation of the cylinders for the fourth examplerolling split lambda fueling schedule 805 are selected such thatcompletion of each fueling schedule avoids emission control devicebreakthrough and achieves substantially stoichiometric conditions at theemission control device.

The fourth example rolling split lambda fueling schedule 805 includesboth stoichiometric and non-stoichiometric engine cycles. In particular,the first engine cycle 840 and the fourth engine cycle 846 arestoichiometric engine cycles, while the second engine cycle 842 and thethird engine cycle 844 are non-stoichiometric engine cycles.Specifically, the second engine cycle 842 is lean and the third enginecycle 844 is rich, with a percentage lean of the second engine cycle 842equal to a percentage rich of the third engine cycle 844. Because thepercentage lean of the second engine cycle 842 and the percentage richof the third engine cycle 844 are equal, the second engine cycle 842 andthe third engine cycle 844 average to stoichiometry. For example, thenumber of rich cylinders included in both the second engine cycle 842and the third engine cycle 844 is one half of the number of leancylinders included in both the second engine cycle 842 and the thirdengine cycle 844. Because the rich cylinders are twice as rich as thelean cylinders are lean, one rich cylinder compensates for one leancylinder to bring the average exhaust gas AFR to stoichiometry acrossthe second engine cycle 842 and the third engine cycle 844. As a result,the fourth example rolling split lambda fueling schedule 805 achievessubstantially stoichiometric conditions at the emission control deviceover the four engine cycle fueling schedule.

In cases where the rich cylinders 836 are operated at 20% rich and thelean cylinders 838 are operated at 10% lean, the first engine cycle 840may be stoichiometric; the second engine cycle 842 may be 10% lean; thethird engine cycle 844 may be 10% rich; and the fourth engine cycle 846may be stoichiometric.

In at least one example, an order of the engine cycles in the fourthexample rolling split lambda fueling schedule 805 may be altered.Moreover, which cylinders are rich and which cylinders are lean withineach engine cycle may be adjusted without departing from the scope ofthis disclosure. That is, in FIG. 8D, the first engine cycle 840 isshown with the far left cylinder as a rich cylinder 836. However, inother examples, the middle cylinder or the right cylinder may be therich cylinder 836.

It is noted that the optimal rolling split lambda fueling schedule wouldbe the one that results in the lowest exhaust temperature (to allowhigher engine loads at higher engine speeds) while meeting bothpredetermined emissions requirements (to avoid catalyst breakthrough andachieve stable combustion) and predetermined NVH requirements.

To maximize the exhaust temperature reduction, approximately equal richand lean biases may be selected since exhaust temperature is roughlysymmetric around stoichiometry. For example, a 20% rich and 20% leanbias may drop exhaust temperature by around 75° C. Thus, a schedule withan equal number of 20% rich and 20% lean cylinders will reduce exhausttemperature by 75° C.

Similarly, a 10% lean bias may drop exhaust temperature by around 30° C.So a fueling cycle with one 20% rich cylinder, and two 10% leancylinders will drop exhaust temperatures by an average of 45° C.

Therefore, if possible, a schedule with equal rich and lean bias may bechosen. But if combustion stability concerns do not allow lean biases aslarge as rich biases (for example, a 20% lean bias may result in poorcombustion stability if used along with EGR), then unequal rich and leanbiases may be selected instead of restricting both rich and lean biases.For example, a 20% rich engine cycle, 10% lean engine cycle, and 10%lean engine cycle fuel schedule results in a lower exhaust temperaturethan a 10% rich engine cycle and 10% lean engine cycle fuel schedule.

Also, choosing an unequal rich and lean bias changes the NVHcharacteristics. First, a larger rich bias than lean bias may reduce thediscrepancy between rich cylinder torque and lean cylinder torque.Second, an unequal rich and lean bias may excite different frequencies(for example a 20% rich engine cycle, 10% lean engine cycle, 10% leanengine cycle repeats every 3 firing events. A 10% rich engine cycle and10% lean engine (or 20% rich engine and 20% lean engine cycle) onlyrepeats every two firing events. Thus, for the same pair of chosen richand lean biases for the engine cycles (example 20% rich and 20% lean),several fueling schedules exist which can excite different frequencies.For example, an alternating one rich cylinder and one lean cylinderfueling RLRL . . . schedule has double the frequency of a two richcylinders and then two lean cylinders fueling schedule RRLLRRLL . . . .Further still, a fueling schedule which carries out one rich cylinder,and then two lean cylinders RLLRLL . . . excites another frequency thatis ⅔ of the one rich cylinder and one lean cylinder RLRL . . . fuelingschedule, which would not be possible to achieve with equal rich andlean biases.

Therefore, one fueling schedule may be selected if it avoids excitingengine resonant frequencies or frequencies causing NVH greater than athreshold. Further, it may be possible for the default split lambda tohave better NVH at some engine operating conditions, while one or moreof the rolling split lambda options may have better NVH characteristicsat other engine operating conditions.

Further, to minimize the risk of catalyst breakthrough, shorterrepeating patterns with shorter sequences of consecutive rich cylindersor consecutive lean cylinders may be selected in at least one example.For example, an alternating one rich cylinder and one lean cylinderfueling schedule RLRL . . . with equal rich and lean biases may beselected over a two rich cylinders, and two lean cylinders RRLLRRLL . .. fueling schedule pattern using same rich and lean biases. Thealternating one rich cylinder and one lean cylinder fueling scheduleRLRL . . . with equal rich and lean biases may also be selected over ora fueling schedule of one rich cylinder, and then two lean cylinderspattern RLLRLL . . . having a rich bias twice as large as the lean biasmay further be preferable over a fueling schedule such as RRLLLLRRLLLL .. . using the same rich and lean biases.

Turning back now to step 512 at FIG. 5, after operating the engine inthe rolling split lambda mode (such as illustrated at FIGS. 8A-8D) withPFI for the rich cylinders and DI for the lean cylinders, method 500 mayend.

Turning back now to step 510 at FIG. 5, if rolling split lambda mode isdetermined not to be optimal for NVH and/or exhaust temperaturereduction (“NO”), then method 500 includes operating the engine in adefault split lambda mode with PFI for rich cylinders and DI for leancylinders at step 514. That is, the engine may simultaneously notbenefit from operating in rolling split lambda mode while dual fuelinjection is available in order for method 500 to carry out step 514.PFI and DI may be carried out in a similar manner at step 514 asdescribed in relation to step 512 and may achieve similar advantages.

Operation in the default split lambda mode may include a default splitlambda mode fueling schedule. The default split lambda mode fuelingschedule operates the engine with at least one non-stoichiometriccylinder per engine cycle while maintaining substantially stoichiometricconditions at the emission control device for each engine cycle. Thatis, in contrast to the rolling split lambda mode where individual enginecycles are non-stoichiometric, the default split lambda fueling schedulemaintains substantially stoichiometric conditions at the emissioncontrol device for each engine cycle.

Looking briefly to FIGS. 9A-9D, example default split lambda modefueling schedules are shown. It is noted that the particular cylindersoperated rich and operated lean in the default split lambda fuelingschedules are for exemplary purposes and may be altered withoutdeparting from the scope of the present disclosure. For example, the twomiddle cylinders are illustrated as operating rich and the two endcylinders are illustrated as operating lean in FIG. 9A. However, in oneor more examples, the two middle cylinders may instead be operated leanand the end cylinders may be operated rich, or every other cylinder maybe operated rich in FIG. 9A, so long as overall stoichiometry ismaintained. Further still, the particular cylinders operated rich orlean may be changed from engine cycle to engine cycle, so long asoverall stoichiometry is maintained. For example, using FIG. 9A as anexample once again, the two middle cylinders may be operated rich andthe two end cylinders may be operated lean for a first engine cycle inaccordance with the first default split lambda fueling schedule 900.Then, still following the first default split lambda fueling schedule900, the two middle cylinders may be operated lean and the two endcylinders may be operated rich for a second engine cycle. Changing whichparticular cylinders are operated rich and which cylinders are operatedlean from engine cycle to engine cycle may advantageously help to avoidissues such as soot buildup, for example. Similar changes also apply tothe examples shown at FIGS. 9B-9D.

Further, similar to step 512, at step 514 the torque output calculationsat step 503 may be compared to the torque demand received at step 502.Then, based on a difference between the torque output calculations atstep 503 compared to the torque demand received at step 502, defaultsplit lambda fueling schedules may be selected and/or created andactions associated with the default split lambda fueling schedules maybe carried out at step 514 (e.g., adjusting VCT, actuating fuelinjectors, adjusting actuation of spark plugs for spark timingadjustments, adjusting a position of an EGR valve, adjusting a positionof an intake throttle, etc.).

Turning now to FIG. 9A, a first default split lambda fueling schedule900 is shown. The first default split lambda fueling schedule 900 is aone engine cycle fuel schedule. In the first default split lambdafueling schedule 900, rich cylinders 902 are denoted via the circleswith hatching and lean cylinders 904 are denoted via solid circles. Thefirst default split lambda fueling schedule 900 is for a four cylinderengine.

In the first default split lambda fueling schedule 900, it is noted thateach of the rich cylinders 902 are operated at a percentage rich that isequal to a percentage lean of each of the lean cylinders 904. Byoperating the rich cylinders 902 at a percentage rich equal to thepercentage lean of the lean cylinders 904, overall stoichiometry isachieved at the completion of each engine cycle.

For example, each of the rich cylinders 902 may be operated at 20% rich(a phi value of 1.20) and each of the lean cylinders 904 may be operatedat 20% lean (a phi value 0.80). Or, in another example, each of the richcylinders 902 may be operated at 15% rich (a phi value of 1.15) and eachof the lean cylinders 904 may be operated at 15% lean (a phi value of0.85).

Further percentage amounts for rich and lean are possible withoutdeparting from the scope of this disclosure, so long as the percentageused for the rich cylinders 902 and the lean cylinders 904 achievesstoichiometry at the completion of each engine cycle. That is, theparticular percentage rich and percentage lean used in the operation ofthe cylinders for the first default split lambda fueling schedule 900are selected such that completion of each engine cycle achievessubstantially stoichiometric conditions at the emission control device.In this way, cooling advantages due to the non-stoichiometric operationof the cylinders is achieved while maintaining overall stoichiometricconditions at the emission control device. Moreover, though illustratedas one bank, it is noted that in at least one example the cylinders atFIG. 9A may be a first bank of a two bank engine configuration. In suchexamples where the cylinders shown at FIG. 9A are a first enginecylinder bank of a two engine cylinder bank configuration, the secondengine cylinder bank may also be operated so that the second enginecylinder bank is overall stoichiometric.

While the first default split lambda fueling schedule 900 is shown withhalf of the cylinders operated rich and half of the cylinders operatedlean, it is noted that there may be an unequal number of rich and leancylinders, in at least one example. In such cases where there is anunequal number of rich and lean cylinders, various percentage amountsfor the rich and lean cylinder operation are possible without departingfrom the scope of this disclosure, so long as the percentage used forthe rich cylinders 902 and the lean cylinders 904 achieves stoichiometryat the completion of each engine cycle.

Turning now to FIG. 9B, a second default split lambda fueling schedule901 is shown. The second default split lambda fueling schedule 901 is aone engine cycle schedule. In the second default split lambda fuelingschedule 901, rich cylinders 906 are denoted via the circles withhatching and lean cylinders 908 are denoted via solid circles. Thesecond default split lambda fueling schedule 901 is for a three cylinderengine. Due to the odd number of cylinders, and the requirement tomaintain substantially stoichiometric conditions at the emission controldevice each cycle, the rich cylinders are unable to be operated at asame percentage rich as the lean cylinders are operated lean. Thus, inthe second example default split lambda fueling schedule 901, it isnoted that the rich cylinder 906 is operated at a percentage rich thatis twice a percentage lean of each of the lean cylinders 908. Byoperating the rich cylinder 906 at a percentage rich twice thepercentage lean of each of the lean cylinders 908, overall stoichiometryis achieved at the completion of the engine cycle. Alternative fuelingratios are also possible, however. For example, in at least one example,there may be two rich cylinders 906 at 15% rich and one lean cylinder908 operated at 30% lean. Other variations as to the fueling ratios arealso possible without departing from the scope of this invention, solong as there is at least one non-stoichiometric cylinder and overallthe fueling schedule 901 maintains substantially stoichiometricconditions at the emission control device. Further, in at least oneexample, the cylinders shown at FIG. 9B may be a first cylinder bank ofa two cylinder bank configuration. In such examples where the cylindersshown at FIG. 9B may be a first cylinder bank of a two cylinder bankconfiguration, the second cylinder bank would also be operated atoverall stoichiometry.

Moving now to FIG. 9C, a third default split lambda fueling schedule 903is shown. The third default split lambda fueling schedule 903 is a oneengine cycle schedule. Thus, the third default split lambda fuelingschedule 903 schematically illustrates operation of a first enginecylinder bank 910 and a second engine cylinder bank 912 for a singleengine cycle. In the third example default split lambda fueling schedule903, each cylinder of the first engine cylinder bank 910 is a richcylinder 914 and each cylinder of the second engine cylinder bank 912 alean cylinder 916. It is noted that reference to rich cylinders hereinrefers to cylinders which are operated at an AFR rich of stoichiometry.However, variations as to the fueling operations for the first enginecylinder bank 910 and the second engine cylinder bank 912 are possible,so long as the percentage rich of the first engine cylinder bank 910 isequal to the percentage lean of the second engine cylinder bank 912. Forexample, if the first engine cylinder bank 910 is operated at 20% richoverall for each engine cycle, then the second engine cylinder bank 912is operated at 20% lean overall for each engine cycle. In this way,substantially stoichiometric conditions are maintained at the emissioncontrol device while achieving cooling advantages due to thenon-stoichiometric operation of the engine. Alternatively, forconfigurations where the engine comprises a first engine cylinder bank910 with four cylinders and a second engine cylinder bank 912 with fourcylinders, each of the first and second engine cylinder banks may befueled in accordance with the approach described in relation to FIG. 9A.That is, each of the first engine cylinder bank 910 and the secondengine cylinder bank 912 may be operated stoichiometrically.

Turning now to FIG. 9D, a fourth default split lambda fueling schedule905 is shown. The fourth default split lambda fueling schedule 905 is aone engine cycle schedule. Thus, the fourth default split lambda fuelingschedule 905 schematically illustrates operation of a first enginecylinder bank 918 and a second engine cylinder bank 920 for a singleengine cycle. In the fourth example default split lambda fuelingschedule 905, rich cylinders 922 are operated at a same percentage richas the lean cylinders 924 are operated lean. Thus, the first enginecylinder bank 918 is enleaned at an amount equal to an amount the secondengine cylinder bank 920 is enriched. Such a fueling schedule results ineach overall engine cycle of the fourth default split lambda fuelingschedule 905 being stoichiometric. For example, the rich cylinders 922may be operated at 10% rich (a phi value of 1.10) and the lean cylinders924 may be operated at 10% lean (a phi value of 0.90) in the fourthdefault split lambda fueling schedule 905. In such examples, the firstcylinder bank 918 would be overall be enleaned by 3.3% (a phi value of0.967) and the second cylinder bank 920 would overall be enriched by3.3% (a phi value of 1.033). Thus, for each engine cycle in the fourthdefault split lambda fueling schedule 905, stoichiometric conditions areadvantageously maintained at the emission control device while stillbenefitting from cooling properties of carrying out non-stoichiometriccylinder operation.

Turning back to step 514 at FIG. 5, after operation of the engine in thedefault split lambda mode (such as shown at FIGS. 9A-9D) method 500 mayend.

Moving now to step 508, should dual fuel injection not be available(“NO”), method 500 includes determining whether the engine is operatingwith rolling split lambda mode conditions at step 516. Rolling splitlambda mode conditions may be engine operating conditions during whichthe rolling split lambda mode is optimal for NVH and/or exhausttemperature reduction. Put another way, responsive to determining thatonly DI is available or that only PFI is available, method 500 moves tostep 516. In some examples, dual fuel injection may be determined asunavailable at step 508 if any of the cylinders do not have one of DI orPFI available. In some examples, such availability may be based on adiagnostic routine for each of the DI injectors and the PFI injectors todetermine functionality of the injectors. It is noted that the dual fuelinjection may be determined as unavailable responsive to a diagnosticindicating that only one of DI injectors (e.g., direct injectors 66) andPFI injectors (e.g., port fuel injectors 67) are available for all ofthe cylinders. Additionally or alternatively, the availability may bebased on a fuel availability for each of the DI injectors and the PFIinjectors in configurations where a fuel source for each of the DIinjectors and the PFI injectors may be separate.

At step 516, the determination as to whether the engine is operating inthe rolling split lambda conditions is as described at step 510. Asdescribed above, the rolling split lambda conditions are engineoperating conditions in which the rolling split lambda mode is optimalfor NVH and/or exhaust temperature reduction. If the engine is operatingin the rolling split lambda conditions at step 516 (“YES”), method 500includes operating the engine in the rolling split lambda mode with PFIor DI for all of the cylinders. That is, the engine may simultaneouslybenefit from operating in rolling split lambda mode while dual fuelinjection is not available in order for method 500 to carry out step518.

At step 518, whichever type of injection is the only injection available(only DI or only PFI) is used for all cylinders at step 518 in therolling split lambda mode. Thus, regardless of whether the cylinders areoperated rich or lean, only one of DI or PFI is used for all of thecylinders at step 518. Aside from using either all DI via the directinjectors or all PFI via the port fuel injectors, step 518 is carriedout in a similar manner as step 512. That is, similar fuel schedules(FIGS. 8A-8D) and other controls as discussed at step 512 may be used atstep 518, with the exception that only DI or only PFI is used. Followingstep 518, method 500 may end.

Turning back to step 516, responsive to determining that the engine isnot operating in rolling split lambda conditions (that is, the rollingsplit lambda mode is not optimal for NVH and/or exhaust temperaturereduction) (“NO”) at step 516, method 500 includes operating the enginedefault split lambda mode either PFI or DI for all of the cylinders atstep 520. That is, to carry out step 520, the engine operatingconditions are such that operation in the rolling split lambda modewould not be beneficial while simultaneously dual fuel injection is notavailable. Similar to step 518, regardless of whether the cylinders areoperated rich or lean, whichever type of injection is the only injectionavailable (only DI or only PFI) is used for the cylinders at step 520.Aside from using either all DI via the direct injectors or all PFI viathe port fuel injectors to perform fueling, step 520 is carried out in asimilar manner as step 514. That is, similar fuel schedules (FIGS.9A-9D) and other controls as discussed at step 514 may be used at step520, with the exception that only DI or only PFI is used. Following step520, method 500 may end.

Moving now to FIG. 10A and FIG. 10B, an example speed-load map 1000 andan example timeline 1002 are shown. Speed-load map 1000 may be stored onthe engine controller for use during engine operation. Timeline 1002illustrates example transitions between operation in the stoichiometric,default split lambda, and rolling split lambda modes based on speed-loadmap 1000. As the speed-load map 1000 and the example timeline 1002 areinterrelated, both FIG. 10A and FIG. 10B are described herein together.

As shown at FIG. 10A, the speed-load map 1000 relates engine speed andload. Engine speed (RPM) increases in a direction of the x-axis arrowand the engine load increases in the direction of the y-axis arrow.Regions labeled II, IV, VI, and VIII of speed-load map 1000, which arefilled with a hatch pattern, correspond to speed-load conditions inwhich a rolling split lambda operating mode is carried out. Regions II,IV, VI, and VIII of speed-load map 1000 form the regions where thestoichiometric mode results in excessive exhaust temperatures, and therolling split lambda mode is more effective compared to the defaultsplit lambda for NVH and exhaust temperature reduction. Regions labeledIII, V, and VII of speed-load map 1000, which are filled with a dotpattern, correspond to speed-load conditions in which a default splitlambda operating mode is carried out. Region labeled I of speed-load map1000, which is filled with a vertical stripe pattern, representsspeed-load conditions in which a stoichiometric operating mode iscarried out. Thus, each of the regions of FIG. 10A represent a set ofengine operating conditions and engine operating modes to be carried outresponsive various engine operating conditions. In at least one example,the regions may be determined based on which engine operating mode ismost effective to reduce NVH and/or exhaust temperature while stillsatisfying torque demands.

As may be seen in FIG. 10A, at loads above a load threshold 1028 at theupper boundary of region I, the rolling split lambda operating mode orthe default split lambda mode is used. Load threshold 1028 also dividesthe rolling split lambda and the default split lambda modes from oneanother. That is, 1028 is not just the upper boundary of region I butincludes all of the heavy lines within the speed-load map 1000 at FIG.10A to divide the regions from one another. Put another way, loadthreshold 1028 is represented by the heavy lines extending betweenregions I, II, III, IV, V, VI, VII, and VIII of speed-load map 1000. Theupper boundary of region I correspond to the torque threshold in 504,while the boundaries splitting the default and rolling split lambdaregions determine the outcome of 510 and 516.

Load threshold 1028 is dynamically updated based on speed. That is, loadthreshold 1028 is not static. For example, the load threshold 1028between region I and region II of speed-load map 1000 is higher than theload threshold 1028 at between region I and region III of speed-load map1000. Though the load threshold 1028 is shown to change substantially atdifferent engine speeds, in at least one examples, the load threshold1028 may be gradually changed as the engine speed changes.

It is noted that the regions illustrated in speed-load map 1000 areexemplary and may be tuned to individual driveline configurations. In atleast one example, the speed-load map 1000 may act as a reference mapwhich is adjusted based on feedback during operation. For example, thespeed-load map 1000 may be stored at factory settings and then may beadjusted responsive to feedback from sensors, such as sensors indicatingNVH, based on engine operation. By adjusting the speed-load map 1000based on feedback from sensors during engine operation, the speed-loadmap 1000 may improve efficiency of the engine operation in differentenvironmental conditions and variance in the driveline configuration. Inat least one example, the load threshold 1028 separating a default splitlambda from a rolling split lambda region may be decreased responsive todetermining that NVH greater than a threshold NVH occurs at an enginespeed where default split lambda or rolling split lambda operating modesare set to be carried out.

Additionally or alternatively, a testing mode may be periodicallycarried out to determine whether or not the load threshold 1028 may beincreased. In at least one example, the increase of the load threshold1028 may not exceed load and speed conditions confirmed to result in NVHgreater than the threshold NVH responsive to the testing mode results.

In at least one example, the threshold separating stoichiometricoperation mode from one of the split lambda modes (e.g., the defaultsplit lambda mode and the rolling split lambda mode) may be changedbased on exhaust temperature considerations. For example, the thresholdseparating stoichiometric operation from one of the split lambda modesmay be adjusted to ensure that engine operation maintains exhausttemperatures less than a threshold exhaust temperature. The thresholdexhaust temperature may be a temperature at which it is determineddegradation of one or more exhaust components may occur. In one or moreexamples, the threshold separating stoichiometric operation mode fromany of the split lambda modes may be changed based on exhausttemperature considerations and not NVH.

Turning now to time t1004 of FIG. 10B, t1004 corresponds to operation ofthe engine in a first condition that is in region I of the speed-loadmap 1000. Dual fueling 1024 is further available at time t1004.

Responsive determining that the engine is being operated in the firstcondition within region I while dual fueling 1024 is available, theengine is operated in the stoichiometric operating mode without dualfueling, as seen at operating mode trace 1020 and dual fueling operationtrace 1022. Such operation may be carried out from time t1004 to t1006.By operating the engine in the stoichiometric mode responsive to thefirst condition that is in region I, emissions may be avoided and engineperformance may be maintained with a reduced risk of overheating theengine components.

At time t1006, the engine is operated in a second condition that is inregion III of the speed-load map 1000. In particular, an engine speedand load increases from t1004 to t1006, such that the engine is operatedin region III. For example, the speed of the engine is increasedresponsive to an increase in torque demand to be greater than thethreshold torque demand. The second condition in region III thusincludes operation of the engine at a speed and load which is higherthan the speed of the first condition in region I. The dual fuelingavailability trace 1026 indicates that dual fueling is still availableat time t1006. In at least one example, dual fueling availability may bedetermined in a similar manner as discussed at step 508 of method 500.Thus, as seen at t1006 of FIG. 10B, the engine is operated in thedefault split lambda mode from t1006 to t1008 with dual fuelingoperation, as indicated by dual fueling operation trace 1022. In atleast one example, the default split lambda operating mode at time t1006may correspond to the default split lambda mode at step 514 of method500. By operating in the default split lambda mode at time t1006 duringthe second condition that is in region III, substantially stoichiometricconditions may be achieved at an emission control device of the enginewhile maintaining engine performance and avoiding overheating of enginecomponents.

At time t1008, the engine is operated in a third condition that is inregion IV of the speed-load map 1000. During the third condition inregion IV at time t1008, a speed of the engine is greater than at timet1006. Further, a load at the third condition in region IV may be lessthan the load of the second condition in region III. This decrease inload may be due to driving the vehicle downhill, in at least oneexample. It is noted that dual fueling is available as indicated by dualfueling availability trace 1024. Responsive determining that the engineis being operated in the third condition in region IV at time t1008 withdual fueling available, the rolling split lambda operating mode iscarried out with dual fueling operation, as seen at operating mode trace1020 and dual fuel operation trace 1022 of FIG. 10B. In at least oneexample, the rolling split lambda operating mode at time t1008 maycorrespond to the rolling split lambda mode at step 512 of method 500.By operating in the rolling split lambda mode at time t1008 as seen attrace 1020, amplification due to resonance may be reduced by carryingout non-stoichiometric engine cycles to alter the driveline frequency.That is, rolling split lambda mode operation may advantageously alterthe fuel schedule frequency to avoid the resonant frequency whilemaintaining substantially stoichiometric conditions at an emissioncontrol device of the engine.

Following time t1008 and the third condition in region IV, the engine isoperated in a fourth condition at time t1010. In the fourth condition inregion VI, a load of the engine is further increased and a speed of theengine increases. In at least one example, the increase in load may bedue to a steepness of a hill the vehicle is driving up increasing. Atthe fourth condition in region VI, the torque demand is still greaterthan the threshold torque demand. Looking to time t1010 of FIG. 10B, thedual fueling availability trace 1024 indicates that dual fueling isstill available.

Responsive operation of the engine in the fourth condition in region VIat time t1010, the rolling split lambda operating mode continues to becarried out with dual fueling operation, as seen at operating mode trace1020 and dual fuel operation trace 1022 of FIG. 10B. Thus, theadvantages and operating action of the engine in the fourth condition inregion VI at time t1010 are similar to the advantages and operatingactions from the third condition in region IV at time t1008.

After time t1010 and the fourth condition in region VI, the engine isoperated in a fifth condition in region V at time t1012. In the fifthcondition in region V, a load of the engine is maintained while anengine speed is decreased. Thus, at the fifth condition in region V, thetorque demand is still greater than the threshold torque demand. As aresult of the operation in region V, the engine is operated withoutexciting the resonant frequency that may cause NVH of the driveline toexceed the NVH threshold. Further, looking to time t1012 of FIG. 10B,the dual fueling availability trace 1026 indicates that dual fueling isstill available.

Responsive determining that the engine is being operated in fifthcondition in region V at time t1012, the default split lambda operatingmode is carried out with dual fueling operation, as seen at operatingmode trace 1020 and dual fuel operation trace 1022 of FIG. 10B. In atleast one example, the default split lambda operating mode at time t1012may correspond to the default split lambda at step 514 of method 500. Byoperating in the default split lambda mode at time t1012, substantiallystoichiometric conditions may be achieved at an emission control deviceof the engine while maintaining engine performance and avoidingoverheating of engine components.

After time t1012 and the fifth condition in region V, the engine isoperated in a sixth condition in region VII at time t1014. In the sixthcondition in region VII, a speed of the engine may be substantiallyincreased and a load decreased from the fifth condition in region V, forexample. In at least one example, the sudden jump in speed from V to VIImay be due to a down-shift. Looking to time t1014 of FIG. 10B, the dualfueling availability trace 1024 indicates that dual fueling is no longeravailable. Determination as to a lack of dual fueling availability maycorrespond to step 508 of method 500, in at least one example.

Responsive determining that the engine is being operated in the sixthcondition region VII at time t1014, the default split lambda operatingmode is carried out without dual fueling operation, as seen at operatingmode trace 1020 and dual fuel operation trace 1022 of FIG. 10B. That is,responsive to being operated in region VII without dual fuelingavailable, the default split lambda operating mode is carried outwithout dual fueling operation at time t1014. In at least one example,the default split lambda operating mode at time t1014 may correspond tothe default split lambda mode at step 520 of method 500. By operating inthe default split lambda mode at time t1014 during the sixth conditionin region VII, substantially stoichiometric conditions may be achievedat an emission control device of the engine while maintaining engineperformance and avoiding overheating of engine components.

Following time t1014 and the sixth condition in region VII, the engineis operated in a seventh condition in region VIII at time t1016. In theseventh condition in region VIII, a speed of the engine is substantiallysimilar to the sixth condition in region VII. However, in contrast tothe sixth condition in region VII, the engine load is increased to begreater than or equal to load threshold 1028 shown between region VIIand region VIII in the seventh condition. As a result, NVH may increaseabove the NVH threshold if engine operation is not adjusted. Further,looking to time t1018 of FIG. 10B, the dual fueling availability trace1026 indicates that dual fueling is not available at time t1018.

Responsive determining that the engine is being operated in seventhcondition in region VIII at time t1016, the rolling split lambdaoperating mode is carried out without dual fueling operation, as seen atoperating mode trace 1020 and dual fuel operation trace 1022 of FIG.10B. That is, responsive to being operated within region VIII, wheredual fueling is not available, the rolling split lambda operating modeis carried out without dual fueling operation. In at least one example,the rolling split lambda operating mode at time t1016 may correspond tothe rolling split lambda mode operation at step 518 of method 500. Byoperating in the rolling split lambda mode at time t1016 during seventhcondition in region VIII, amplification due to resonance may be reducedby carrying out non-stoichiometric engine cycles to alter the drivelinefrequency. That is, rolling split lambda mode operation mayadvantageously alter the driveline frequency to avoid NVH issues.

Following time t1016 and seventh condition in region VIII, the engine isoperated in an eighth condition in region I at time t1018. In the eighthcondition in region I, a speed and load of the engine is decreased to beless than the load threshold 1028 defining the upper boundary of regionI. The eighth condition in region I includes operation of the engine ata speed similar to the engine speed of first condition in region I. Inat least one example, the load of eighth condition in region I may besubstantially the same as the load of the seventh condition in regionVIII. Looking to time t1018 of FIG. 10B, the dual fueling availabilitytrace 1024 indicates that dual fueling is not available at time t1018.

Responsive determining that the engine is being operated in the eighthcondition in region I at time t1018, the stoichiometric operating modeis carried out without dual fueling operation, as seen at operating modetrace 1020 and dual fuel operation trace 1022 of FIG. 10B. That is,responsive to being operated with the torque demand less than athreshold torque demand defining the upper boundary of region I, wheredual fueling is not available, the stoichiometric operating mode iscarried out without dual fueling operation. In at least one example, thestoichiometric operating mode at time t1018 may correspond to thestoichiometric mode operation discussed at step 506 of method 500. Byoperating the engine in the stoichiometric mode responsive to the eighthcondition in region I at time t1018, emissions may be avoided and engineperformance may be maintained with a reduced risk of overheating theengine components.

Thus, provided herein are systems and methods for carrying out splitlambda fueling operations for an engine to address issues such as NVHdue at least in part to split lambda fuel schedules exciting engineresonant frequencies. In at least one example, the rolling split lambdamode may be used instead of default split lambda mode during a conditionwhere split lambda operation enables higher torques. Thus, the rollingsplit lambda mode may be carried out during one or more of the followingconditions: a rolling split lambda fueling schedule is predicted toimprove NVH compared to the default split lambda mode, and the rollingsplit lambda mode enables higher engine torques than the default splitlambda mode.

An example method includes, while operating an engine in a conditionthat is within a resonant frequency region for a default split lambdamode, carrying out a rolling split lambda mode, wherein the engine isoperated with only stoichiometric engine cycles in the default splitlambda mode, the stoichiometric engine cycles including enleaned andenriched cylinders, wherein the engine is operated with a plurality ofnon-stoichiometric engine cycles when carrying out the rolling splitlambda mode, the plurality of non-stoichiometric engine cycles includingat least one rich engine cycle and at least one lean engine cycle. In afirst example of the method, the condition includes a torque commandgreater than a threshold torque demand. In a second example of themethod, which optionally includes the first method, the plurality ofnon-stoichiometric engine cycles are part of a predetermined number ofengine cycles, and wherein the predetermined number of engine cyclesresult in overall stoichiometric conditions at the emission device ofthe engine. In a third example of the method, which optionally includesone or both of the first and second examples, the resonant frequencyregion of the default split lambda mode is an operating region of theengine in which an amount of NVH is greater than a predetermined NVHthreshold when carrying out the default split lambda mode. In a fourthexample of the method, which optionally one or more of the first throughthird examples, the rolling split lambda mode has a higher torque outputpotential than the default split lambda mode while operating the enginein the condition. In a fifth example of the method, which optionallyincludes one or more of the first through fourth examples, whileoperating the engine outside of the resonant frequency region of thedefault split lambda mode with a torque demand greater than a thresholdtorque demand, the fifth example of the method includes carrying out thedefault split lambda mode in which every engine cycle is stoichiometric.In a sixth example of the method, which optionally includes one or moreof the first through fifth examples, carrying out the default splitlambda mode includes non-stoichiometric operation of one or morecylinders of the engine.

In a further method, which optionally includes one or more features ofthe above-discussed method, the method comprises operating an engine ina condition where one or more of a potential torque output of a defaultsplit lambda mode is less than a potential torque output of a rollingsplit lambda mode, and operation in the default split lambda mode isdetermined to cause NVH greater than a threshold; and while operatingthe engine in the condition, carrying out the plurality ofnon-stoichiometric engine cycles in the rolling split lambda mode,wherein the engine is operated with only stoichiometric engine cycles inthe default split lambda mode, the stoichiometric engine cyclesincluding enleaned and enriched cylinders wherein the engine is operatedwith a plurality of non-stoichiometric engine cycles when carrying outthe rolling split lambda mode, the plurality of non-stoichiometricengine cycles including at least one rich engine cycle and at least onelean engine cycle. In a first example of the method, the conditionincludes an engine torque demand that is greater than a threshold torquedemand. In a second example of the method, which optionally includes thefirst example, the engine is operated within a resonant frequency regionfor the default split lambda mode in the condition. In a third exampleof the method which optionally includes one or both of the first andsecond methods, the third example of the method further comprisesoperating the engine in a further condition where the engine torquedemand is less than the threshold torque demand, and operating allcylinders of the engine at stoichiometry in a stoichiometric mode duringthe further condition. In a fourth example of the method, which includesone or more of the first through third examples, a different fuelingschedule is used to deliver fuel to cylinders of the engine in thedefault split lambda mode than in the rolling split lambda mode.

An example system, which may include a controller configured to carryout one or more of the above-discussed methods, comprises an engine,wherein the engine includes a plurality of cylinders; a plurality offuel injectors coupled to the engine; an emission control devicepositioned downstream of an exhaust manifold of the engine; a controllerwith computer readable instructions stored on non-transitory memorythat, when executed during engine operation, cause the controller to:calculate a first potential torque output of a default split lambdamode, wherein the engine is operated with only stoichiometric enginecycles in the default split lambda mode, the stoichiometric enginecycles including enleaned and enriched cylinders of the plurality ofcylinders; calculate a second potential torque output of a rolling splitlambda mode, wherein the rolling split lambda mode includes carrying outa plurality of non-stoichiometric engine cycles; and carry out theplurality of non-stoichiometric engine cycles via the rolling splitlambda mode responsive to the second potential torque output beinggreater than the first torque output. It is noted that the system mayinclude instructions in the controller to carry out one or more of thesteps discussed above in the example method, as well as any furtherexample methods discussed herein. In a first example of the system, theinstructions further cause the controller to carry out the plurality ofnon-stoichiometric engine cycles via the rolling split lambda moderesponsive to the engine being operated in a condition which isdetermined to cause greater than a threshold amount of NVH if the engineis operated in the default split lambda mode. In a second example of thesystem, which optionally includes the first example, the engine isdetermined to be operating within the condition which causes greaterthan the threshold amount of NVH based on a speed and a load of theengine. In a third example of the system, which includes one or both ofthe first and second examples, carrying out the plurality ofnon-stoichiometric engine cycles via the rolling split lambda modeincludes carrying out at least one lean engine cycle and at least onerich engine cycle. In a fourth example of the system, which optionallyincludes one or more of the first through third examples, a differentfueling schedule is used to deliver fuel to the plurality of cylindersof the engine in the default split lambda mode than in the rolling splitlambda mode. In a fifth example of the system, which optionally includesone or more of the first through fourth examples, completion of theplurality of non-stoichiometric engine cycles in the rolling splitlambda mode results in substantially stoichiometric conditions at theemission control device. In a sixth example of the system whichoptionally includes the first through fifth examples, the sixth examplesystem further comprises a first exhaust manifold and a second exhaustmanifold, wherein the first exhaust manifold and the second exhaustmanifold are coupled to different cylinders of the plurality ofcylinders. In a seventh example of the system, which optionally includesone or more of the first through sixth examples, the first exhaustmanifold and the second exhaust manifold are upstream a turbine of theengine, and wherein the first exhaust manifold and the second exhaustmanifold combine upstream of the turbine via a junction. In an eighthexample of the system, which optionally includes one or more of thefirst through seventh examples, a singular passage extends fromdownstream the junction to the turbine, and wherein the emission controldevice is positioned downstream the turbine.

Additionally, provided herein are methods and systems for calculatingtorque outputs in a split lambda mode, such as the split lambda modesdiscussed above. For example, a method comprises, via a controller,operating an engine with one or more non-stoichiometric cylinders of aplurality of cylinders; calculating a stoichiometric torque output ofthe plurality of cylinders; then applying one or more lean torquemodifiers for every lean cylinder of the one or more non-stoichiometriccylinders to the stoichiometric torque output to calculate a lean torqueoutput; separately applying one or more rich torque modifiers for everyrich cylinder of the one or more non-stoichiometric cylinders to thestoichiometric torque output to calculate a rich torque output; summingthe lean torque output and the rich torque output to calculate a totalengine torque output; comparing the total engine torque output to adesired torque output; and adjusting one or more of an amount of fueldelivered to the plurality of cylinders and spark timing based on thecomparison. In a first example of the method, applying the one or morelean torque modifiers to every lean cylinder includes applying the oneor more lean torque modifiers to every lean cylinder individually, andadjusting the one or more lean torque modifiers prior to the individualapplication of the one or more lean torque modifiers, the one or morelean torque modifiers adjusted based one or more parameters of the leancylinder to which the one or more lean torque modifiers are beingapplied. In a second example of the method, which optionally includesthe first method, the one or more parameters of the lean cylinderinclude an air-fuel-ratio of the lean cylinder. In a third example ofthe method, which optionally includes one or both of the first andsecond methods, calculating the total engine torque output includesgrouping the one or more non-stoichiometric cylinders into a richcylinder group and a lean cylinder group, wherein applying the one ormore lean torque modifiers for every lean cylinder includes applying theone or more lean torque modifiers to the lean cylinder group to form alean cylinder group torque output, and wherein applying the one or morerich torque modifiers for every rich cylinder includes applying the oneor more rich torque modifiers to the rich cylinder group to form a richcylinder group torque output. In a fourth example of the method, whichoptionally includes one or more of the first through third methods,summing the lean torque output and the rich torque output to calculatethe total engine torque output includes summing the rich cylinder grouptorque output and the lean cylinder group torque output. In a fifthexample of the method, which optionally includes one or more of thefirst through fourth examples, the one or more rich torque modifiersincludes one or more of a rich cylinder group spark timing and a richcylinder group air-fuel-ratio, and where the one or more lean torquemodifiers includes one or more of a lean cylinder group spark timing anda lean cylinder group air-fuel-ratio, wherein each of the one or morenon-stoichiometric cylinders of the rich cylinder group has a sameamount of rich bias, and wherein each of the one or morenon-stoichiometric cylinders of the lean cylinder group has a sameamount of lean bias. In a sixth example of the method, which optionallyincludes one or more of the first through fifth examples, adjusting theamount of fuel delivered to the plurality of cylinders includesadjusting actuation of one or fuel injectors of the engine, and whereinadjusting the spark timing includes adjusting actuation of one or morespark plugs of the engine.

In an example, a system comprises an engine, wherein the engine includesa plurality of cylinders; a plurality of fuel injectors coupled to theengine; a controller with computer readable instructions stored onnon-transitory memory that, when executed during engine operation, causethe controller to: operate an engine with one or more non-stoichiometriccylinders of a plurality of cylinders; calculate a stoichiometric torqueoutput of the plurality of cylinders; then apply one or more lean torquemodifiers for every lean cylinder of the one or more non-stoichiometriccylinders to the stoichiometric torque output to calculate a lean torqueoutput; separately apply one or more rich torque modifiers for everyrich cylinder of the one or more non-stoichiometric cylinders to thestoichiometric torque output to calculate a rich torque output; sum thelean torque output and the rich torque output to calculate a totalengine torque output; compare the total engine torque output to adesired torque output; and adjust one or more of an amount of fueldelivered to the plurality of cylinders and spark timing based on thecomparison. It is noted that the system may include instructions in thecontroller to carry out one or more of the steps discussed above in theexample method, as well as any further example methods discussed herein.In a first example of the system, the instructions further cause thecontroller to, in response to carrying out a rolling split lambda mode,apply the one or more lean torque modifiers to every lean cylinderindividually, and adjust the one or more lean torque modifiers prior tothe individual application of the one or more lean torque modifiers, theone or more lean torque modifiers adjusted based one or more parametersof the lean cylinder to which the one or more lean torque modifiers arebeing applied, wherein the rolling split lambda mode includes carryingout a plurality of non-stoichiometric engine cycles. In a second exampleof the system, which optionally includes the first example, theinstructions further cause the controller to, in response to carryingout the rolling split lambda mode, apply the one or more rich torquemodifiers to every rich cylinder individually, the one or more richtorque modifiers adjusted prior to the individual application of the oneor more rich torque modifiers, the one or more rich torque modifiersadjusted based on one or more parameters of the rich cylinder to whichthe one or more rich torque modifiers are being applied. In a thirdexample of the system, which optionally includes one or both of thefirst and second examples, the one or more parameters of the leancylinder and the one or more parameters of the rich cylinder include anair-fuel-ratio. In a fourth example of the system which optionallyincludes one or more of the first through third examples, the fourthexample further comprises one or more lean torque modifiers for everylean cylinder and applying one or more rich torque modifiers for everyrich cylinder includes applying the one or more lean torque modifiers toa lean cylinder group to calculate a lean cylinder group torque output,and applying the one or more rich torque outputs to a rich cylindergroup to calculate a rich cylinder group torque output. In a fifthexample of the system, which optionally includes one or more of thefirst through fourth examples, summing the lean torque output and therich torque output to calculate the total engine torque output includessumming the lean cylinder group torque output and the rich cylindergroup torque output. In a sixth example of the system, which optionallyincludes one or more of the first through fifth examples, the one ormore lean torque modifiers include one or more of a spark timing torquemodifier and an air-fuel-ratio torque modifier.

In a further method, which may include one or more of theabove-discussed features, the comprises, via a controller, operating anengine with one or more non-stoichiometric cylinders of a plurality ofcylinders; calculating an average cylinder torque output based on acurrent engine speed, a current engine load, a current variable camtiming (VCT), and a total number of the plurality of cylinders; thenapplying one or more lean torque modifiers to the average cylindertorque output for each lean cylinder of the one or morenon-stoichiometric cylinders to calculate a lean cylinder torque output;applying one or more rich torque modifiers to the average cylindertorque output for each rich cylinder of the one or morenon-stoichiometric cylinders to calculate a rich cylinder torque output,calculating a total engine torque output based on the lean cylindertorque output and the rich cylinder torque output; comparing the totalengine torque output to a desired torque output; and adjusting one ormore of an amount of fuel delivered to the plurality of cylinders andspark timing based on the comparison. In a first example of the method,values associated with the one or more lean torque modifiers are basedon a lambda value of the lean cylinders of the one or morenon-stoichiometric cylinders. In a second example of the method, whichoptionally includes the first example, values associated with the one ormore rich torque modifiers are based on a lambda value of the richcylinders of the one or more non-stoichiometric cylinders. In a thirdexample of the method, which optionally includes one or both of thefirst and second examples, applying the one or more lean torquemodifiers includes applying includes applying a lean air-fuel-ratiotorque modifier value to the lean cylinders of the one or morenon-stoichiometric cylinders, and wherein applying the one or more richtorque modifiers includes applying a rich air-fuel-ratio torque modifiervalue to the rich cylinders of the one or more non-stoichiometriccylinders. In a fourth example of the method, which optionally includesone or more of the first through third examples, all the lean cylindersare grouped separately from all the rich cylinders prior to applying thelean air-fuel-ratio torque modifier and the rich air-fuel-ratio torquemodifier. In a fifth example of the method, which optionally includesone or more of the first through fourth examples, applying the one ormore lean torque modifiers and applying the one or more rich torquemodifiers includes individually applying an air-fuel-ratio torquemodifier value to each of the one or more non-stoichiometric cylinders.

Additionally or alternatively, described herein are systems and methodsfor operating the engine with PFI and DI, such as during the splitlambda mode. A first example of the method comprises while operating anengine with at least one lean cylinder and at least one rich cylinderdelivering fuel to the at least one lean cylinder via direct fuelinjection (DI) and delivering fuel to the at least one rich cylinder viaport fuel injection (PFI). In a second example, which optionallyincludes the first example, the method further comprises transitioningthe at least one rich cylinder fueled via PFI to instead be operated atstoichiometry, and fueling the at least one rich cylinder transitionedto be operated at stoichiometry via DI. In a third example of themethod, which optionally includes one or both of the first and secondexamples, the at least one rich cylinder is transitioned responsive to atorque demand decreasing from above a threshold torque demand to belowthe threshold torque demand. In a fourth example of the method, whichoptionally includes one or more of the first through third examples, thefourth example includes performing a PFI and DI diagnostic, determiningthat PFI is not available, and then fueling both the at least one leancylinder and the at least one rich cylinder via DI. In a fifth exampleof the method, which optionally includes one or more of the firstthrough fourth examples, the engine is operated with the at least onelean cylinder and the at least one rich cylinder responsive to a torquedemand greater than a threshold torque demand. In a sixth example of themethod, which optionally includes one or more of the first through fifthexamples, operating the engine with the at least one lean cylinder andthe at least one rich cylinder includes operating the engine in arolling split lambda mode, where the rolling split lambda mode includescarrying out a plurality of non-stoichiometric engine cycles. In aseventh example of the method, which optionally includes one or more ofthe first through fifth examples, operating the engine with the at leastone lean cylinder and the at least one rich cylinder includes operatingthe engine in a default split lambda mode, where the default splitlambda mode includes only carrying out stoichiometric engine cycles. Inan eighth example of the method, which optionally includes the firstthrough seventh examples, DI is carried out via direct fuel injectors,and wherein PFI is carried out via port fuel injectors which aredifferent than the direct fuel injectors.

An example system is further disclosed which includes, an engineincluding a plurality of cylinders; a plurality of direct injectors,each direct injector coupled to one of the plurality of cylinders; aplurality port fuel injectors, each port fuel injector coupled upstreamof each of the plurality of cylinders; and a controller with computerreadable instructions stored on non-transitory memory that, whenexecuted during engine operation, cause the controller to: whileoperating the plurality of cylinders with at least one rich cylinder andwith at least one lean cylinder, delivering fuel to the at least onerich cylinder via the corresponding port fuel injectors and deliveringfuel to the at least one lean cylinder via the corresponding direct fuelinjectors. It is noted that the system may include instructions in thecontroller to carry out one or more of the steps discussed above in theexample method, as well as any further example methods discussed herein.In a first example of the system, the computer readable instructions,when executed during engine operation, further cause the controller to:operate the plurality of cylinders at stoichiometry, and deliver fuel tothe plurality of cylinders via the corresponding direct injectors. In asecond example of the system, which optionally includes the firstexample, the plurality of cylinders are operated at stoichiometryresponsive to a torque demand less than a threshold torque demand. In athird example of the system, which optionally includes one or both ofthe first and second examples, the plurality of cylinders are operatedwith the at least one rich cylinder and the at least one lean cylinderduring operation in a rolling split lambda mode, wherein there are aplurality of non-stoichiometric engine cycles in the rolling splitlambda mode, and wherein only stoichiometric engine cycles are carriedout in a default split lambda mode. In a fourth example of the system,which optionally includes one or more of the first through thirdexamples, the plurality of cylinders are operated with the at least onerich cylinder and the at least one lean cylinder during operation in thedefault split lambda mode. In a fifth example of the system, whichoptionally includes one or more of the first through fourth examples,the rolling split lambda mode is carried out responsive to one or moreof operating the engine in a resonant frequency region of the defaultsplit lambda mode, and a potential torque of the rolling split lambdamode being greater than the potential torque of the default split lambdamode. In a sixth example of the system, which optionally includes one ormore of the first through fifth examples, the engine is determined to beoperated in the resonant frequency region of the default split lambdamode based on an engine speed and an engine load. In a seventh exampleof the system, which optionally includes one or more of the firstthrough sixth examples, the computer readable instructions, whenexecuted during engine operation, further cause the controller to: carryout a diagnostic for dual fuel injection, wherein the dual fuelinjection is available responsive to both the direct injectors and theport fuel injectors being operable, and wherein the dual fuel injectionis unavailable responsive to only one of the direct injectors and theport fuel injectors being operable; determine that the dual fuelinjection is unavailable; and continue operating the plurality ofcylinders with at least one rich cylinder and with at least one leancylinder, delivering fuel to the at least one rich cylinder and to theat least one lean cylinder using port fuel injection.

In a further example a method comprises, while operating a plurality ofcylinders of an engine with at least one rich cylinder and with at leastone lean cylinder, delivering fuel to the at least one rich cylinder viaport fuel injection (PFI) and delivering fuel to the at least one leancylinder via direct fuel injection (DI); and determining that one of PFIand DI is no longer available, and delivering fuel to all of thecylinders via only PFI or only DI. In a first example of the method,operation of the plurality of cylinders with at least one rich cylinderand with at least one lean cylinder is responsive to a torque demandgreater than a threshold torque demand. In a second example of themethod, which optionally includes the first example, delivering the fuelto all of the cylinders via only PFI or only DI is carried out whilestill operating the plurality of cylinders with at least one richcylinder and at least one lean cylinder. In a third example of themethod, which optionally includes one or both of the first and secondexamples, the plurality of cylinders are operated with at least one richcylinder and at least one lean cylinder responsive to a torque demandgreater than a threshold.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The control methods and routines disclosed herein may be stored asexecutable instructions in non-transitory memory and may be carried outby the control system including the controller in combination with thevarious sensors, actuators, and other engine hardware. The specificroutines described herein may represent one or more of any number ofprocessing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various actions,operations, and/or functions illustrated may be performed in thesequence illustrated, in parallel, or in some cases omitted. Likewise,the order of processing is not necessarily required to achieve thefeatures and advantages of the example embodiments described herein, butis provided for ease of illustration and description. One or more of theillustrated actions, operations, and/or functions may be repeatedlyperformed depending on the particular strategy being used. Further, thedescribed actions, operations, and/or functions may graphicallyrepresent code to be programmed into non-transitory memory of thecomputer readable storage medium in the engine control system, where thedescribed actions are carried out by executing the instructions in asystem including the various engine hardware components in combinationwith the electronic controller.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

As used herein, the term “approximately” is construed to mean plus orminus five percent of the range unless otherwise specified.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

The invention claimed is:
 1. A method comprising: while operating anengine in a condition that is within a resonant frequency region for adefault split lambda mode and in which a rolling split lambda mode iscalculated to reduce an exhaust temperature of the engine compared tothe default split lambda mode, carrying out the rolling split lambdamode and reducing the exhaust temperature of the engine, wherein theengine is operated with only stoichiometric engine cycles in the defaultsplit lambda mode, the stoichiometric engine cycles including enleanedand enriched cylinders, and wherein the engine is operated with aplurality of non-stoichiometric engine cycles when carrying out therolling split lambda mode, the plurality of non-stoichiometric enginecycles including at least one rich engine cycle and at least one leanengine cycle.
 2. The method as claimed in claim 1, wherein the conditionincludes a torque command greater than a threshold torque demand.
 3. Themethod of claim 2, wherein the plurality of non-stoichiometric enginecycles are part of a predetermined number of engine cycles, and whereinthe predetermined number of engine cycles result in overallstoichiometric conditions at an emission device of the engine.
 4. Themethod of claim 3, wherein the resonant frequency region of the defaultsplit lambda mode is an operating region of the engine in which anamount of NVH is greater than a predetermined NVH threshold whencarrying out the default split lambda mode.
 5. The method of claim 1,wherein the rolling split lambda mode has a higher torque outputpotential than the default split lambda mode while operating the enginein the condition.
 6. The method of claim 1, further comprising: whileoperating the engine outside of the resonant frequency region of thedefault split lambda mode with a torque demand greater than a thresholdtorque demand, carrying out the default split lambda mode in which everyengine cycle is stoichiometric.
 7. A method comprising: operating anengine in a condition where one or more of a potential torque output ofa default split lambda mode is less than a potential torque output of arolling split lambda mode, and operation in the default split lambdamode is determined to cause NVH greater than a threshold; and responsiveto and while operating the engine in the condition, carrying out theplurality of non-stoichiometric engine cycles in the rolling splitlambda mode and reducing an exhaust temperature of the engine, whereinthe engine is operated with only stoichiometric engine cycles in thedefault split lambda mode, the stoichiometric engine cycles includingenleaned and enriched cylinders wherein the engine is operated with aplurality of non-stoichiometric engine cycles when carrying out therolling split lambda mode, the plurality of non-stoichiometric enginecycles including at least one rich engine cycle and at least one leanengine cycle.
 8. The method of claim 7, wherein the condition includesan engine torque demand that is greater than a threshold torque demand.9. The method of claim 8, wherein the engine is operated within aresonant frequency region for the default split lambda mode in thecondition.
 10. The method of claim 9, further comprising, operating theengine in a further condition where the engine torque demand is lessthan the threshold torque demand, and operating all cylinders of theengine at stoichiometry in a stoichiometric mode during the furthercondition.
 11. The method of claim 7, wherein a different fuelingschedule is used to deliver fuel to cylinders of the engine in thedefault split lambda mode than in the rolling split lambda mode.
 12. Asystem, comprising: an engine, wherein the engine includes a pluralityof cylinders; a plurality of fuel injectors coupled to the engine; anemission control device positioned downstream of an exhaust manifold ofthe engine, wherein the emission control device comprises one or more ofa catalyst brick and a particulate filter; a controller with computerreadable instructions stored on non-transitory memory that, whenexecuted during engine operation, cause the controller to: calculate afirst potential torque output of a default split lambda mode, whereinthe engine is operated with only stoichiometric engine cycles in thedefault split lambda mode, the stoichiometric engine cycles includingenleaned and enriched cylinders of the plurality of cylinders; calculatea second potential torque output of a rolling split lambda mode, whereinthe rolling split lambda mode includes carrying out a plurality ofnon-stoichiometric engine cycles; carry out the plurality ofnon-stoichiometric engine cycles via the rolling split lambda moderesponsive to the second potential torque output being greater than thefirst potential torque output; and carry out the plurality ofnon-stoichiometric engine cycles via the rolling split lambda mode andreducing an exhaust temperature of the engine responsive to the enginebeing operated in a condition which is determined to cause greater thana threshold amount of NVH if the engine is operated in the default splitlambda mode.
 13. The system of claim 12, wherein the engine isdetermined to be operating within the condition which causes greaterthan the threshold amount of NVH based on a speed and a load of theengine.
 14. The system of claim 12, wherein carrying out the pluralityof non-stoichiometric engine cycles via the rolling split lambda modeincludes carrying out at least one lean engine cycle and at least onerich engine cycle.
 15. The system of claim 14, wherein a differentfueling schedule is used to deliver fuel to the plurality of cylindersof the engine in the default split lambda mode than in the rolling splitlambda mode.
 16. The system of claim 12, wherein completion of theplurality of non-stoichiometric engine cycles in the rolling splitlambda mode results in substantially stoichiometric conditions at theemission control device.
 17. The system of claim 12, further comprisinga first exhaust manifold and a second exhaust manifold, wherein thefirst exhaust manifold and the second exhaust manifold are coupled todifferent cylinders of the plurality of cylinders.
 18. The system ofclaim 17, wherein the first exhaust manifold and the second exhaustmanifold are upstream a turbine of the engine, and wherein the firstexhaust manifold and the second exhaust manifold combine upstream of theturbine via a junction.
 19. The system of claim 18, wherein a singularpassage extends from downstream the junction to the turbine, and whereinthe emission control device is positioned downstream the turbine.